There's a repost of an interesting newsgroup post by 3dfx chief scientist Gary Tarolli over at The Pulpit, where he talks about how hardware T&L can decrease the longevity of a videocard, instead of increase it. Here's a snip from his argument

So why would a Voodoo5 have a longer life span than a card with T&L? One reason is because it's feature-proof, as strange as that may seem. Hardware T&L cards like the GeForce have their feature set pretty much frozen. For example, the GeForce supports lerping between 2 matrices from what I understand, and no more. Developers basically cannot use this feature, and require 4 matrices at a minimum. When APIs support this, the GeForce will have to fall back to software T&L or not expose the feature. The Voodoo5 uses software T&L all along and thus can implement any feature that comes along. Basically hardware T&L will accelerate (and even that is questionable) today's features only. Once new features come along, these cards will either not support the feature or fall back to software t&l. Note: this is for gfx chips that are hardwired, ie. not microcoded, heavily microcoded chips can implement most new features in microcode. So I would argue that hardware T&L does not increase longevity and can actually shorten it.

update Jack - Now before you make all sorts of rash judgements about what he's saying, go and actually read the entire post. While I am neither agreeing nor disagreeing with Gary, I must say that this snip does not do his argument justice.