It's a good question, and it's a topic that you simply won't even be exposed to if you're purely an Apple product user.
Setting up your choices as a $50 clunker or a newish car is a false dichotomy that doesn't exist in car purchases and doesn't exist in computing. For $500 I can buy a laptop that will let me do everything I want to do hobbywise. That means I can buy a new one every year for six years, meaning I'll get better hardware every year for more than half a decade, before I hit the price of my bottom spec rMBP I got last year. Are they not as nice pieces of hardware? Sure! But at that price I don't care, I'm getting what I pay for. There is simply no reliable low mileage $3500 used Honda Accord option in the Apple world.
Most Mac software I've run across that I'd describe as "hobbyist" are either ports of open source projects or "scratch an itch because OS X or the default app suite it ships with is broken".
Rather than go into a list that would go on forever, I'd ask this, what hobbyist software communities can you not participate in because you're on a mac?
Think about how many times you or somebody around you has said "doh! too bad I'm on a mac" and then think of that time as the tip of an iceberg with a catalog of whatever software that goes into the tens or hundreds of thousands.
Okay now some examples:
Or consider this one example among thousands. Suppose I'm into old Japanese Games (niche, but there's a hobbyist community around it) and want to play the Sharp X68000 Castlevania Chronicles because it exists nowhere else. I turn to emulation and find at least 5 emulators for the platform on Windows, 2 or 3 of them are actually pretty good. There's 1 for OS X and it doesn't work all that well and the community hasn't even bothered translating the docs from Japanese. Or even worse, for the Playstation 2, there are 0 emulators.
Or suppose I want to participate in the Demoscene, put my coding skills to the test, that sort of thing. In 2013 there were 15 releases in the community. By way of comparison, there were about 20 linux releases in the same time period. On Windows there's been 15 releases this month and something north of 8,000 releases in 2013. The Amiga has a more vibrant community in this milieu than the Macintosh does.
Things are better if you're a musician in the scene, there's a handful of trackers available for OS X, and they're pretty good ones. But let's say I want to support my team and help with making a 4k intro. There are no tools available on the Mac for writing 4k music. That's cool, I'll help out with the regular music and start grabbing VSTis and VSTs...ooooh...95% of the hobbyist community's VST work is done with Windows and they don't work on OS X without a bunch of kludges (if they work at all). Here's the current instructions for a somewhat workable solution http://diaphone.blogspot.de/2010/12/11.html?m=1 on OS X.
And the age-old games ecosystem.
And these are just the 3 hobbies I personally follow. I have an Aunt who has an automated sewing machine and like making patches and things for her grandkids. AFAIK there are zero tools on OS X for this hobby. And the list goes on and on and on.
It's just not a good platform for these kinds of hobbies. If I was really into writing or painting or more "analog" hobbies, OS X is awesome for this. If I was into configuring LAMP stacks and such, it's pretty good. But outside of that it's a near barren wasteland.