Have you tried manually syncing your Google Account on the Nexus to try to force it to pull them down? If it's not so many, you can log into GMail on your Mac and add them manually. If it's a lot, I'd verify they synced with your GMail at all.
It looks like contacts was not turned on for my Google account! So confusing. Why are there as many contacts as there are then?
Anyway, I turned it on. I tried checking via the web, but the contacts still haven't synced. I'll try again later and see if the missing people come in.
Confusing...
doug