Because most web site designers assume 96DPI and set font sizes in pixels?
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.
Every web browser can zoom in on documents. I set default zoom to 150%. dpreview.com looks fine.
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.
"Because most web site designers assume 96DPI and set font sizes in pixels?"
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.
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.