if we follow that reasoning we 'll need a different list for each 1.9 release as none of those are incompatible either.. most popular should imo be linked only to a modules downloads.. some modules provide releases for 1.8 and 1.9 releases at the same time, some don't, shouldn't affect what s considered popular.. those that do are more likely to attract more downloads too.
the idea s fundamentally flawed imo because there are even a number of modules that ll work on 1.8.0, but not on 1.8.6 (without having been updated).