1st grandchild due in 2 weeks and there has been no mention of when I will be able to see the baby for the first time. I asked about the possibility of my visit when the baby is 2-3 weeks old and was told "We'll talk about it" and that was 3 weeks ago. No further mention has been made by me or my son and daughter-in-law. I guess I just wait for an invitation?

Yes, you just have to wait patiently.
If you care to talk about any strained relations, feel free.
There's also the logistics of going out there, getting a ride from the airport, a place to stay, how much you need in the way of daily routine events like meals and use of bathrooms or ways to get back to a hotel, whether you drive, all sorts of things that might hamper an already exhausting new existence for the couple.
Long distance often boils down to the parents needing help vs the grandparents just wanting to see the baby. It sounds cruel but it's merely practical survival at a tough time.

Plus, you have internet, so ask for videos and pictures when they have a chance, or if they use Facebook, keep watching and commenting there, and keep it positive and happy.

After just giving birth and all of the issues, having a out of town house guest is about the last thing a new mother wants. If no invitation after a couple months, just invite yourself, tell them you will be out... for a visit.

Plus, you have internet, so ask for videos and pictures when they have a chance, or if they use Facebook, keep watching and commenting there, and keep it positive and happy.

Thanks, joypulv! I am acquainting myself with Facebook this week!