An interesting observation on the current crop of top PC chess programs. Rybka, the program that tops all the ranking lists, does so with a node count that is much lower. That is, Rybka looks at around a tenth of the number of positions per second compared to other programs. The reason is does so well, is that it has a very sophisticated evaluation algorithm for each position it examines. In some sense, it has better chess knowledge than other programs.
And this is the difference between Kasparov and Deep Blue (and other chess computers). The computer can analyse millions of positions per second. Kasparov might examine only a couple of positions per second, but he does so with far greater knowledge and insight - he recognizes when pieces are coordinated and mobile, when pawn structures are strong, when his king is safe.