I received legit copies of 3.5 and 3.9 with machines I picked up, but never use them. They don't seem to offer much when your best machine has a 68030, and they won't even run on the machine I usually use. I'm the same way on the Macintosh. I own or can legally download more recent versions of the OS, but stick to the older ones because they will run better on my older hardware.
But just because I own them and don't use them doesn't mean that I'll get rid of them. OS 3.9 is way too expensive (IMHO). I wouldn't want to pay to replace it down the road, so I may as well keep my copies in the off chance I did want to use them.