When did he state that?
From the Bitcoin 0.1.0 release notes:
Operating Systems
-----------------
Windows NT/2000/XP (and probably Vista)
Vista hasn't been tested yet. All the libraries used are cross-platform, so
there's nothing preventing future Linux and Mac builds.
Compilers Supported
-------------------
MinGW GCC (v3.4.5)
Microsoft Visual C++ 6.0 SP6
You can't be sure only with these information.
For example, i could make these speculation.
1. Satoshi use older compiler so more programmer could compile Bitcoin source code.
2. Satoshi don't bother test on Vista due to low Vista user or that would take too much time.