Whats the reason PS3 owners not buying Dragon Age?

[Reasonable]

The key reasons, as noted by many, are:

1 - 360 has better install base for WRPGs, particularly in US, and the developer is better known on 360 side vs PS3

2 - PS3 demographic, probably combined with 1) above, does seem to skew more to JRPG vs WRPG

3 - PS3 version shipped at a relatively bad time relative to other PS3 exclusives and big multi-platform titles

I think it's actually sold okay on PS3 all things considered, particularly in relation to relative install base ratio, it's just that in terms of raw sales units 360 has the advantage for this type of title currently.