1. Disenchanted 40K players(I used to be one) considering another system.
2. Would-be wargamers deciding on which game to pursue.
So here are my five top reasons(yes the list could be longer)...
1. Game Rules: Let's cut to the chase...if you are going to play a miniature wargame, a solid ruleset is a must. Warmachine is known for its easy to learn, yet sophisticated, rules set. Warhammer 40K is known as a clunky system which invites debate over not just the proper application of the rules as written, but the logic behind them. Now I could give a plethora of examples but let me pick one of my favorites. In 40K a unit chooses whether to use a cover save or an armor save(whichever is most advantageous to the defending unit)...this make no sense(wouldn't an armored space marine still benfit from the cover of a crater in addition to his armor?). In Warmachine the armor and cover are treated separately(through ARM and DEF) so that this is not an issue, and the matter is dealt with more logically. It's amazing that after FIVE editions and decades of experience GW could still have such a messy, contentious rules system...while in far less time, and just two tries...Privateer Press has a tight, functional, logical model for wargaming.
2. Entry Cost: Essentially a player can begin Warmachine for approximately $40(give or take) with a BattleBox. A player can start 40K with a set like Black Reach, but we're talking about $100. Now a GW loyalist will say "But WM is a skirmish game and 40K is a large scale wargame". Well that's fine but let's be honest about that scale. Purchasing Black Reach means you've got a small starting force for only Orks or Space Marines...you'll need to spend another $100 U.S. to even begin to flesh out that force to competitive standard. The WM player can easily expand their force in significant ways with a much smaller investment. Also, the would be WM(and Hordes) player can pick up a battlebox for the faction of their choice to get started...they are not limited to the two in a starter set. Even with the upcoming WM starter set(which is two factions), PP will continue to offer the battleboxes and warpacks as a more flexible way to enter the hobby.
3. Internet Friendly: Games Workshop seems to hate the internet. From their own horrible website, their restrictions on image usage, to their shafting of online retailers with highly restrictive policies, they have a great 1986 business model. Privateer Press seems to embrace this modern medium. They have forums(visited by their actual employees) which are a great source of knowledge and advice(and an avenue for customer feedback). GW uses their website as catalog...and that's about it. Now there are some really nice "third party" sites out there like Bell of Lost Souls that promote 40K, but the that same site is often visited by Privateer Press employees who comment on articles about their product line(you don't see that from the GW folks). Here is a great video from miniwargaming.com that goes into detail on some of GW's ridiculous policies.
4. Support Materials: Privateer Press publishes a high quality rulebook and forces(faction) books. Compare your average WM or Hordes forces book to a 40K codex and you'll see a huge difference in quality...especially in terms of color images and the helpful hobby(painting) section in all the PP supplements. I remember dropping $20 for a thin, little Tau codex that later looked pathetic next to my Forces of Khador book(I've since sold my off all my 40K stuff).
5. Release Calendar: This is, to me, the clincher. Warhammer 40K is currently using their 5th edition rulebook. Now since the release of this book(two years ago) they have gradually updated their armies with codex releases staggered over time. Two years later there are still armies that are not up to date with their 'latest' rules system. I knew someone who had a fairly useless Dark Eldar army that they held on to for a year and then sold off in frustration(the codex was hopelessly outdated for the previous 40K edition)...months later the new Dark Eldar codex came out that made their army competitive. Now there are rumors of a 40K 6th edition...so the ridiculous cycle can start all over again. I am so thankful I am now fully invested in Warmachine. Within six months Privateer Press published their second edition rules and faction books for all related armies. Their ambitious release schedule for 2nd edition had the whole game system updated in a short time...while 40K's 5th edition came out well before WM mark II and still all the 40K armies aren't updated all this time later. I could compare the advertisement called "White Dwarf" to the magazine entitled "No Quarter" as an additional illustration of this point...but I think I'd be beating a dead horse.
So what happens from here? Well, I expect that Privateer Press will continue to increase their market share and a lot of people will make the switch from 40K to, quite frankly, the better game. Now if you love the lore or the minis of the 40K universe then go about your business(and clunky rules) so you can enjoy the fantasy world of your choice. However, if you are disenchanted by that game, or deciding which one to pursue, please consider the above. I fall in the former group...although technically historical wargaming was my entry into the miniature wargaming hobby, 40K baptized me in fantasy(scifi) wargaming. However, between the awkward rules, feeling I was being overcharged for product and the problems with the calendar for release of support materials, I looked for a better game...Warmachine was that better game. In a way I'd like to thank GW for driving me away...because you really drove me to seek out a better experience.
If you are interested, here is a video where I described my switch over a year ago...
Iron Kingdoms at War: Superior Ruleset