If the price for the OS was like MS's OS prices then it would annoy me, but they're not anywhere as bad as that. I think it's a bit of a cheapo thing to do, and lacks professionalism. But, provided that the CD came with some kind of proof of authenticity that would be enough for me. After considering the cost of that though, it would probably be cheaper to come up with a 'real looking' pressed CD :-)
Software Hut are selling OS 3.9 for $47 (USD). Windows 2000 goes for anywhere between £100 - £250 UK pounds. Slight difference :-)
Are you getting what you paid for, is the question at the end of the day. Did you pay $40 to look at a nice pressed CD, or to have an operating system on your Amiga hardware?