Macs freeze, too... 🙄
Apps freeze/crash every now and then, but just very rarely will they bring the system down with them. Most often you can "just" kill (force quit) the frozen app (even Finder if that hangs) and your Mac will run happily on. But sometimes the System freezes up, too and you need to do a hard restart (hold power button in for 4-5 seconds to shutdown or in extreme cases pull the power cord (and battery if you have a 'Book)).
Even rarer are Kernel Panics (where the screen dims down and a multilingual message tells you to restart your Mac). They can be caused by faulty software, but repeated Kernel Panics most likely are sign of hardware error, and you should, immediately, backup all your data and get it serviced. I've had one Kernel Panic with my 19 month old iBook, more than a year ago, probably caused by BitTorrent (which also was to blame last time it froze), Bits on Wheels does not freeze my system... 😉 I also had a few on my old Pismo, probably caused by a faulty 3rd party HD, that I finally got replaced.