And I'm not denying that they come from the same wafer in some cases (generally parts in the middle of a wafer are faster, ones on the outside edge much slower).
And whether or not you think a part makes it to 800MHz is mostly due to the fact that when you overclock your expectations are much lower than someone who buys it retail in, say, a Dell computer.
For one thing, the part needs to work at 800MHz for 7 years... you probably don't care about this, but CPU's do slow down with time (I can get you references for this too). So, in 7 years you may not be able to run your 600E at 800MHz, but Intel guarantees that theirs will. Most of the people on this BBS upgrade frequently, but my father still has a working 80286 that they use to do some work at his business...
Second, you may need to increase the voltage on your part to get it to 800MHz (which dramatically cuts the lifetime of the part), or put a bigger heatsink on it (which costs you, the enduser, more money), or you may need to get a special motherboard (one with particularly good bypass cap on it), or you may need special memory, etc. And a lot of threads on here run something along the lines of "I have a Malaysian WW32 SLQUR - I heard this OC's well, but mine won't even do 650MHz. What am I doing wrong." People hunt for specific steppings, SSpec's, production weeks and packaging sites. I know most "normal" people at home wouldn't put up with this stuff. They want to pay money and have it work right the first time.
Third, in your case, if it processor crashes occassionally, well, you tweak it a little and hope for the best. If it crashes a lot, you sell it to someone and buy another one. Hobbyists do it because it's their hobby, but a person who buys a Pentium III 800MHz and has problems with it is going to complain and return it.
My point is that your expectations are fairly low. Intel's corporate customers have very high expectations for reliability. When you are overclocking you are eating into this margin and hoping for the best. It's a risk and you do it because you think it's fun (or at least not totally frustrating) and you think it saves you money.
But the fact that overclocking is possible doesn't change the point of my arguement that Intel tests it's Pentium III 800's and stands by the marking put on the chip. This means that a Pentium III 600E is not the same identical chip as a Pentium III 800EB. In fact, a Pentium III 800EB is inherently worth much more because other people know that it will work reliabily and consistently at 800MHz. So, the author is wrong.
I personally don't overclock my machine. Aside from the fact that Intel gives me fast processors to play with, I use it to work from home. Uptime is hugely important to me. I don't have time to fiddle with my machine, and when I get a blue screen (which fortunately never happens to me with Win2k) I know that I should be cursing Bill G. and not poking around to see if MBM thinks my CPU temp is too high.