I think we are all way over analyzing this whole thing trying to be the ethics police and armchair lawyers and such. Getting a XC under your belt is only a matter of 50 miles, even with an few approaches this can be done in less than 2 hours if you have another airport close enough. I know what your going to say, "But 'I' don't have one that close. I'm just talking in generalities here. There are plenty of things that can be discussed on the 30-40 min cruise portion of a short XC!

I'd be willing to bet if you just talk to your students about it, they would be willing to go an extra .3 or .4 to get that XC in THIER logbook as well, especially if they are planning on making flying a career. If they are, they will need the 500 XC also.

When I was working on my instrument I insisted my instructor make the flights XC because I knew I would need it and I wanted the experience. Doing the same ILS and VOR approach 40 times then taking a check ride on that same ILS is doing nobody any good.