From my own perspective:
i've stopped buying unpainted metal/plastic minis, i have enough to last ten livetimes painting them (to any standard). I'm not saying i won't buy anymore i'm saying that i'll only buy if i'm certain that i'll paint them in the short term. Add to that that i haven't painted in a while (i'm pretty certain that most of my GW paints have dried up) and need to invest in some new painting supplies.
When i look at my former D&D games i used mostly fantasy minis. Low level monsters come in larger lots, painting twelve+ orcs might be fun the first couple of orc, but when you also have to do the 12+ goblins, human bandits, etc, etc. Painting becomes a chore, add to that that i'm not a great painter or a speed painter, a lot of metal minis ended up bare on the table. That doesn't help player immersion.
When prepainted plastics showed up enforce i gave them a look over (mageknight) and was very disapointed, man where those paintjobs crude, i would be better off if i dipped my own in the paint pots... Add to that that the ones that were accaptable were rares and extremely expensive.
Then WotC came out with the D&D minis game, was a little better then mageknight, but still a very bad paintjob. A few expansions later (Archfiends i believe) i was tempted to buy a few packs, the paint job was a lot better, but still not impressive. I was torn, but let my players decide, when they came across the hill giant they blew a casket and were sold. I've been buying cases of the stuff ever since (although i haven't played D&D for a while).
In short: They are relatively cheap when compared to metal (and GW plastics), don't eat up a lot of your time for painting (save money on painting supplies), easy to store (i store them in plastic bags in big plastic boxes), can be thrown at annoying players without breaking or (permanently) poking out an eye ;-)
Same goes for the Star Wars minis, i always wanted some of those old SW minis, they were either unavailable or extremely expensive. Add to that the fact that they were rather small compared to the current day 'standard' of 30mm. And you'll have one disappointed SW fan...
Although i would have bought some metal storm troopers if they came out, i would never have bought the cases of SW minis i have now (i have three AT-ATs standing on a pile of gaming material for example).
I love the Rackham minis, but i currently don't have the inclanation to paint them, thus i'm not buying them, thus i'm not playing the gave (repeat circle). Same goes for Warmachine. If Rackham came out with prepainted minis, they are afordable, nice, and the game is fun/challanging i'll buy some (and knowing rackham, i'm certain that they'll deliver on most aspects i find important).
I'm also a long time Battletech fan, 10-20 years ago you couldn't get your paws on any BT minis. And if you could you would pay through the nose for them, so i have very few actual mechs. Since the WizKids released MechWarrior: Dark Age i bought a case, was disappointed, but saw the potential. A couple of months ago i bought some 200 WMDA minis for less then 1/10 of the 'new' value, there's some interesting stuff in there that might entice me to some conversion work and actual painting...
Battlefield Evolution sounds like a newer version of Armageddon (their mech game), if so, and the mechs were on scale with the classic Battlemechs, were kewl, nicely painted and not to expensive, they might draw a lot of mecha/BT fans...
I think that most companies that sell prepainted minis are aiming for folks that have more disposable income then time (meaning time to paint mini compared to what an hour costs them) amd people that have no inclination/talent to paint minis. There are a lot of people out there that are interested in playing with minis but are discouraged when they find out that they need to paint themselves (or find out that painting minis takes actual skill). Add to that a collectability factor and an arms race fator to it and you insure that people buy a lot and will keep buying them. Thus making large production runs possible, making them cheaper to make, making them more afordable for people that don't have a lot of disposable income...
I'm also looking forward to the SW space ship game, i'm not overly concerned about costs (assuming that they keep it close to the othe SW game), i am concerned about scale...
Just my few euro cents...