I think certain games fail to chart for a number of reasons. Enslaved might have suffered a bit due to a bad release date and having namco bandai as their publisher. Sony or Microsoft alone probably could have done a much better job marketing the game as a must-have rather than a "rental".
I think some people get the allure that a game is better than average if it is 1st party published. If they see a few versions of the game on multiple platforms they probably think less of it. In a way though, not having to make a game across two platforms can benefit a game as you can use a console's strengths with no other hardware compromises in mind.
Bayonetta was completely made with the 360 in mind according to DF while the PS3 wasn't even taken into consideration... and the 360 version flourished for this reason. The sales on both consoles sucked however. Vanquish if im certain is sub-hd on both consoles, and imo was downgraded in order to make the versions identical. And that game didn't sell anything either.
So what is the solution in these cases? Going exclusive? Im not sure really... Go for parity on both consoles, multiplatform release, and sell crappy? Or go for exclusive release, and sell crappy? Its a tough choice.