Guys with 15" 1680x1050 laptops, can you tell me if you're comfortable reading dpreview.com with default font settings?
Every OS that I know of offers scalable fonts
There are more to it than just scalable fonts. Windows is essentially hardwired to 96dpi, only fonts scale, everything else does not: there are virtually no vector graphics involved in traditional Win32 UI API, even icons are fixed bitmaps: 16x16, 32x32, 48x48 or 64x64 pixels. They have some logical units of measurement of dialog boxes, but everything else is measured in pixels, see GDI/GDI+. Switching to 120dpi on windows is downright painful: a lot of applications either start to look ugly and disproportional or sometimes even break down: UI layouts fall apart.
PS. Windows 7 has a proper scalable interface. I don't or use like Windows, but I tried it and it works well. You don't even need to restart the entire OS to change the setting anymore either.
It's sad, but I had to lecture a web designer where I work. It's amazing how he insisted that was the only way and how every monitor in the planet should be set at the same density.
In what way does a higher resolution hurt anything?