Are all the monsters listed on DDI from pre-essentials/MM3 utilizing the updated math/sats? Or were they copied wholesale from their original appearance and left that way?
Some monsters were errata'd (usually in groups, so the foulspawn in the MM1 have been updated) and some that pop in later adventures have been updated too.
Most haven't, and use the old appearance and numbers. Not that updating them without software is difficult.
Most of the time you can just customize a monster, level it up, level it down and save it and it's good. I just tested it with a green dragon, and it's attacks went from 1d10 + 6 to 2d8 + 11 (there were other changes as well). I don't think it does the defense changes for solos properly tho.