I've been involved in flash game creation, and it's absolutely pure game development, if done well. It has larger user base than each of the other platforms mentioned, so I would care mostly about that.
This judgement also befalls java,
according to some. Is it because in
flash its so easy to draw graphics and
to import and add on to the stage any
element we want and also because flash
needs a 'container program' to run and
When I have worked in a team developing flash games, we did it using solely AS3 programming, the graphics production had a custom pipeline(we did not use the Flash editor), as happens in several developments out there(so, no import into stage, and not even using the "standard way" of doing flash...). The result was quite eficient in performance, although if there is a difference, is indeed that matter: performance in the flash player plugin is very far from what you get by doing native binaries with other languages. Also, it's clearly something initially started/thought for just multimedia content addition, not for games from start, and suffers a lot from that. But actually, this makes developers work even harder, so saying doing flash games is not making real games, or not "the real thing", etc...That would far from true.
Anyway, the average earning with those games, can be way lower than getting a publishing deal in console games, etc. (unless being very lucky) And it's getting crowded.
It'd be also false the same statement said about java (being it not 'propper' game development,e tc). It's more about how you deal with it, market considerations, etc.