I personally think it's a bad idea.... If a game goes multiplatform, the PC version will sure to be pirated or being distributed through torrents. Hence, gamers will obviously get the PC version instead of console version.

PC ports such as Prince of Persia was directly ported from the console version. Hence, it can only display resolution of up to 1280x720 only. WTF!!  (I swear to god I am not throwing in a penny for UBISOFT titles ever again).

Games on consoles offers better piracy protection especially on PS3 where until now, there's no fake copies of games available on this platform.

Multiplatform games will hinder and prevent developers from maximizing a console's hardware capabilities. (They need to detune the software so that it is able to run on weaker consoles).

These are a few points that i am able to think of... anyone have more comments to be made, please post... I would gladly hear comments from other gamers.