Netbooks are less likely to be installed using the CD (no built in
optical drive) so if someone does have a 32bit netbook they want to do a
fresh install on they still can download the 32 bit iso and put it on USB.
Have you tried a 64 bit install on a netbook? Seems fine to me on the
netbooks and Atom desktops I have tried, but I have not done a
scientific performance comparison, it just works fine.