You have instant, unlimited access to the required hardware, but the same isn't always true of games. For those, you have to rely on either a physical store (which requires travel time, and which is often closed) or a digital download, which will take 3-4 hours on an average broadband connection. Plus install times for each method.

Even if you don't use OnLive for your primary gaming experience, it still makes sense to install it, and use their free demos to try out new games. Or to plunk down a couple dollars to play a cheap game that you don't feel like going out to buy.

As to needing powerful hardware for non game related reasons, that's not likely to be the case for long. Cloud technology is already in place. There's no reason your computationally intensive tasks need to be done on your desktop. I work as a programmer in North Carolina, and I do almost all of my work (including computationally intensive building/compiling of software) on virtual servers whose physical hosts reside in Texas. Obviously your company may not have such an infrastructure in place yet, but trust me, they will soon. It's simply far more efficient (and cost effective) to do it that way. You won't be "stuck" upgrading your machine for non game related reasons for long.