I think he's trying to make his wife what she isn't: an early adopter. The mainstream wants something that their other mainstream (not early adopter) friends are also using. The early adopters are revolutionaries. The mainstream likes status quo. But that's true about every single technology. Facebook has gone through this, too. Twitter, as well. Would your mom or wife use Twitter in the first year after Twitter launched? But I think Google+ transition to mainstream will be pretty smooth, because it's a great and easy to use product, and it's just a matter of having enough early critical mass to get everyone to hear about it.
You raise some good points about Facebook and Twitter going through the same cycle. I can't think of a service that people adopted immediatelyl; strangely, I can think of a few devices.
it's just a matter of ... get[ting] everyone to hear about it.
That's very true as well, but Google+ has something Facebook (and Twitter et al) didn't -- google.com integration and exposure [1].
Yes, deep integration with all other Google-services gives it advantage over others. Gmail, Calendar with social.. sounds awesome (Really like hangouts)
http://www.quickmba.com/marketing/product/diffusion/