@kylie - I guess that is your opinnion. I'm almost 100% sure that the parasite we see in RE5 is a new and improved version of Las Plagas though. I vividly remember reading that in a document. There is also mad hintage at Umbrella when you are fighting Krauser in RE4.
and the re-releases had Ada's story which was mad RE related, but I guess we can't realistically count that as a part of the main RE4 plot.
Fuck man RE4 was such a better game! Real puzzles, scary at times, the main character was cool instead of Vin Diesel/Arnold mix like someone said above. I loved the story too which you seem to hate like mad.