A scam?

I have a few computers and my older computer happens to be a business model HP with 96mb memory (64+32). I upgraded the system to Windows XP Pro and we know that 96mb memory won't cut it. So I put my own 256mb PC 133 Crucial SDRAM in the slot that had the 32MB DIMM in it and booted the computer up no problem. Computer registered 320MB memory (256+64). Perfect. Then I took that module of PC133 memory and put it in my moms system since she really needed it.

So I went to Best Buy and spent $49 on 256mb PC133 SDRAM to put in my system so that I will be back up to 320mb Ram. I noticed right off the bat that the packaging for this name brand PNY memory clearly stated "For use in 133mhz systems only." I disregarded it since I thought that PC133 memory is backwards compatible with PC100 memory. This has always been the case on systems I've used and built in the past for friends/co-workers. So I installed it into my system and PC would not even Boot!! So I thought it may be an incompatibility with the other memory in the other slot. So I took the other memory chip out and now only the PNY memory was in there and it still would not boot. So I took off to my office and installed it in my PC there (which has 100mhz bus) and NO BOOT either!! WHY IS IT THAT MY OWN PC133 MEMORY FROM CRUCIAL CAN RUN ON SYSTEMS WITH 100MHZ BUSES YET THIS STORE BOUGHT PNY PC133 MEMORY CANNOT?!?. No time to ponder it though so I exchanged it and got the same brand memory but this time stated on the packaging PC100 memory. But check this out: the packaging said "For use in both 100 & 133mhz systems." I shook my head and looked again. Sure enough, the packaging stated that this PC100 memory can run on a 133mhz bus!! What the hell? And to make matters worse this memory even though 256mb as well cost $20 more!! Sound fishy? I think it does. Sounds to me like PNY is putting some sort of bus frequency detecting deal in its chips FORCING you to purchace a different, and possibly, more expensive chip from them. Hit the website or your local store and check this out. I would scan the package for you but scanner is broke. What are your thoughts on this?