OS X has supported x86_64 applications since 10.5 (Leopard), so there's no problem there if your CPU supports it; moreover, the last OS X release to support 32-bit-only x86 CPUs was 10.6 (Snow Leopard). However, Chrome does support 10.6, so I guess this release may have the effect of dropping support for some Mac models from 2006 that previously worked.