@DeathByVisualStudio: My main development machine is using 193GB. Both Program Files directories (it's a 64bit install) total about 16GB. So, 45GB is used for the exact same thing as is used on the Surface Pro. OK, not quite. My desktop doesn't have the 8GB recovery partition... but I blow that off of Surface as well. So, 45GB - 8GB + 16GB means not including data I'll use roughly 53GB of the 128GB drive, leaving me 75GB of space for data. Obviously my current desktop is using more than that, but it's data. On can put data offline in various ways: cloud, SDXC card, USB HD, etc. There's very little in my current 193GB that I'd need/want to have on the main storage of the device.
Microsoft hasn't screwed anything up here. There's no difference between the Surface Pro and any other PC, be it laptop, ultrabook, tablet, desktop or server. There's nothing new here. 128GB is small, but usable, and anyone with an ounce of common sense knows that nothing has changed with the "revelation" here. I'm going to replace my desktop with a device like this. Doesn't matter if it's the Surface or one of the competing devices, they will all have the same storage characteristics. And these numbers have been basically the same for years. Windows 7 had the exact same footprint.
And before you claim Windows is bloated and other's are doing better, the MacBook Air has roughly the same characteristics. The 128GB MBA has 93GB free when you purchase it. That's 9GB difference, which is almost entirely accounted for by the recovery partition, where Apple provides an over the air recovery option. We can argue about that 9GB and whether or not it would be better to not have a recovery partition (there's pros and cons, and I won't argue which is the "right" choice), but the reality is that 9GB is roughly 7% of the space and not very relevant, especially when you realize you have the option to reclaim every bit of that space.