We live 200 miles from our DGC. We see then on average every six weeks. They spent a 5 days with us at Christmas and I am going up for half-term. However we do sit down and plan visits together, the next visit being planned as the previous one ends, because, as both DS & DDiL have outside interests as well as work, and both sometimes work weekends, plus we also have activities that restrict our availability, we find getting everything in the diary well in advance means we do all see each other regularly. There is more to our family than just GC, we enjoy both our son and DDiL's company and like seeing them.
We also have the problem that DS is not good at ringing or talking on the phone, but I think that is, generally, a man thing. As DDiL works part time I quite often ring her on her no-working days and have a good natter. We also email DS regularly, just in a chit chat way, not just when we need to communicate.
I think keeping in touch is something that has to be worked at. I grew up in a forces family. We were always on the move so family visits were planned and organised as both my parents were close to their families. We too did not live near Grandparents and DH travelled abroad a lot, so again visiting used to be planned. It is just automatic that we act in a similar fashion with our DS and family.