Deep Blue was specialized hardware and was created solely for the match. So it may have been tuned to play anti-human chess (i.e. lots of tactics and avoiding closed positions). Note also, it wasn’t until about 2007 when PC chess programs attained the same strength (i.e. just above the same strength as humans). Interestingly, we are at this stage now with Shogi (see here http://goo.gl/L1s8t), where the best computer engines are about the same strength as the best human Shogi players.