I have an MD, two MSes, and a PhD, so I think it's actually quite likely that I've had more "grad school experience" than most of you. That being said, I'm not looking to get into a pissing contest with anyone, especially regarding something as subjective as whether grad school is "hard" or a "real job." The points I'm making are these:
1) For the OP's wife, grad school *is* her job, and it *is* a real job in the sense that it requires her to be certain places at certain times doing certain things in order to progress through her program. It's obviously possible to flunk out of grad school just like it is possible to flunk out of med school or be fired from residency. Depending on what type of degree she is pursuing, her grad school may not be very much like the first two years of med school at all in terms of how it's set up. Unlike med students, as a grad student, OP's wife may also have other work responsibilities such as teaching UGs/TAing, which is a common way for grad students to earn their living expense stipends. If she's doing research, her PI may have expectations regarding when she must be physically present in the lab. And so on.
2) While her schedule is likely to be more flexible overall, there will be times when his is easier than it is at other times as well. It's simply not true that every rotation during residency is equally as hard and time-consuming as every other. Likewise for grad school. During the times when his schedule is easier, it's not unreasonable for him to make a bit more effort so that they can be together, especially if she's in the middle of say, preparing for her thesis defense. Obviously when he is on a tough PICU month or other time-intensive inpatient rotations, she will need to do more driving, or they will need to spend some time apart.
3) My advice was for them not to get a house at all, but rather two small apartments. He really just needs somewhere to crash close by the hospital for those times when he can't drive home. He doesn't need a "house" there. (I actually don't think residents should buy houses at all in most cases, but that's an argument for another time.)