Depends on where you mark success at. If it's to become a commercial success, yes, it's possible to make a breakthrough hit and get commercial success from just being a hobbyist developer. But in general most developers that get respect and recognition are hardcore about their hobby. Still, some developer blogs that talk about hardcore topics already tend to be in the software industry.

Of course if you're not careful, as this article shows, you can be stuck in the "idealist zone" and just work on complex ideas that take too long to flesh out, while the more opportunist types that are interested in making something quick just to get their name out there (and usually money on the side). Some of those "quick buck" developers aren't even hardcore. Stick to your true interests, but don't stay a complete idealist because sooner or later you need to make the jump to getting your stuff out there.

Moving to Lounge.

It heavily depends on which game developing instruments you choose. For example it is much more simple to develop games using Flash and ActionScript, than to learn C++ and make big 3D shooters. But there is nothing impossible.

I think if your are a hobbyist you can be successful (depending on your definition of successful). I for one like most have a day job, wife, a kid etc and develop games on my spare time (usually when our son is down and my wife is at the gym or doing errands). I usually only put forth about 10 hours a week on game development. The point is that you can be successful no matter what (in the definition of building a game) it will just take you longer in the sense of days because you do have all of these other priorities.

It definitely takes work to be successful. You need to put in a lot of hours to complete a project and then you need to spend time to get it out there so that people will hear about it. I often wonder if there is a way to hook up with a school or students that could do some of the "leg work" for me so that I can focus on development rather than all the other bits of game development.