The main reason you are seeing these differences is that Corgi typically prototype each of their models in resin before going ahead with production. The resin models are all hand-painted (sometimes with the nasty cockpit seams you mentioned) to finalize the paint scheme(s) to be used. These same prototypes are then photographed and used for promotional materials and box art, rather than waiting for the first production models to roll off the line. The result is that the finished models often look better than those in the photographs. I've often thought this to be a strange marketing tactic but I guess the deadlines take priority sometimes.
As for buying online, the trick is to find an online store that goes to the trouble of taking their own photographs of the models they sell. It's far easier to scan or copy the promotional photos and box art, so there aren't too many of us that do it; but if you dig around a little, you should find what you're looking for!
Cheers,
Martin.
