As long as it's a form of creative self-expression, anything can be art, but video games, as they're made now, are overwhelmingly not self-expression in any way (although some of their parts are), so they're not actually art. Not even close.
It's not a really good debate though. Once there's a game that's on par with what's generally considered art, people will recognise it, but right now, trying so hard to prove that our favourite pastime is somehow more than pure (and awesome) entertainment just makes people look completely stupid. When you're saying Flower or Braid is "art", you're implicitly comparing them to stuff with achievements like Faust or the Iliad or Citizen Kaine, and in this case the comparison does indeed become pathetic.
As for the argument that video games have had no time to develop, I don't think it's a really good one. The development of any human creation doesn't mainly depend on the physical passing of time, but on human-time, the amount of time individual people have put into it. Games don't develop just because time passes, they develop because people put work-time into them, so that's what counts most imo, and in that respect, games have been doing pretty well. They're just way too difficult to make, even Flash games require some technical knowledge, and I think that's probably a huge barrier.
Also, it's not really easy to say what opportunities the video game form gives to artists. There are of course a few concepts that work better in this form, but overall, it's not an easy question, and I don't know if there really are topics and themes that can be obviously best approached with video games. Most of these topics would fit movies equally well or even better. The choices you can make in video games and the complexity of possible outcomes actually limits artistic freedom, unless you focus on the rules governing the world and the behaviour that emerges from these rules, which is imo not something a lot of people are interested in.
So, overall, right now, we don't know what topics fit the video game form the best, tools are often not artist-centered but focus more on technology, making games requires specialist knowledge and/or loads of resources and there aren't too many games that are "obviously" art.