Libramarian
Adventurer
I think this is an interesting point. The scientific names for the dinosaurs are, in many cases, following a formulaic construction that does much the same thing as the compound words in the 4e monster manuals: they describe the animal in question. They just do so in a fancy-pants manner designed to make the person using them look all the smarter for knowing an archaic language's roots. Because we all know that things sound more exotic when they aren't in our own vernacular even when they're saying much the same thing. N'est-ce pas?
Ultimately, I don't think the 4e-style compounds are doing anything wrong, per se. Rather, they just sound silly when used for creatures that we already have suitable names for.
I don't speak any other languages fluently but something tells me that languages like Latin (and maybe German?) are constructive in such a way that you're supposed to make up new compounds a lot, whereas in English with our ginormous polyglot vocabulary there's no need to do that and it sounds childish. Although dinosaur names are literally simple compound descriptions in Latin, I don't think they have the same connotation of simple-mindedness in Latin as they do in English.
I think for English speakers, because we have so many words with roots in different languages, we have more of a taste for exotic-sounding words than speakers of other languages. Adjective Coolname doesn't cut it, perhaps especially for us.
That's my theory anyway.