Why is IEx64 not the default for x64 Windows?

Solution 1:

I guess it's becoming less of an issue these days, but initially there were no plugins that supported native 64-bit browsers (so you couldn't see Flash animations in 64-bit IE, for example.) So that's most likely why 32-bit is default.

Edit: I haven't actually tested a native 64-bit browser for a while, but since Adobe has said they're working on a native 64-bit player for a year now I assumed it must be out, but that might not be the case. Does anyone know?

Solution 2:

It's for compatibility for add-ons. Most add-ons do not have 64-bit equivalents, or users do not realize they need a 64-bit version of a plugin. Since more laptops are shipping with 64-bit OS's, to keep compatibility issues to a minimum, 32-bit IE is considered standard.