A Curious Anomaly in AMD vs. Intel

At a recent get-together, a bunch of IT people were asked about their preference in processor technology. Not surprisingly, Intel was the most preferred and AMD was all but left in the low-end bargain bin.

This observation is not new by any means, and I personally subscribe to this way of thinking. What strikes me as interesting though, was this recently "ZDNet article about the Cray XT5 Jaguar":http://blogs.zdnet.com/gadgetreviews/?p=9469&tag=nl.e589:

bq. Irrelevant factoid that may only interest me: Four of the top five systems are based on AMD tech, while 402 of the top 500 are powered by Intel.

I'm not sure of the author's numbers, but here is what "the November top500.org list":http://www.top500.org/list/2009/11/100 has. In the US AMD has 4 of the top 10. PowerPC has 3. Intel has 2. PowerXCell (IBM) has 1.

Why is it that the IT masses think that AMD processors are low-end value processors but yet they power 4 out of the top 10 supercomputers in the US?