just like buying glass, you get what you pay for. if you need a tripod for shooting stills indoors, then you don't need a gitzo necessarily. if you are hiking and want to shoot on a rocky slope, then a gitzo makes sense.
lighter, sturdier, taller, etc. all make a tripod more expensive. not everyone needs it, but some do. not all people need a 600mm lens, but some do.
I have owned a gitzo and it was excellent, worth the money to get a rugged, light set of legs with a lifetime warranty. However, it was more than I needed so I "downgraded" to something that fit my needs better.
Have Tom (Sirrith) post some photos of what he does to his tripods in the field and then ask if a $100 dolica could do that