"Since the industry doesn't use Gimp, those students would be putting themselves out of the market."
no. I'm saying since the industry doesn't use gimp, it's not in the best interest for the students to use it either.
How Photoshop actually became the industry standard is another topic.
If a whole graduating class used Gimp, the whole graduating class would be disappointed when they went to find a job and couldn't find one due to lack of experience.
Students don't set the industry standard. They follow it.
I don't think this is entirely true, which is one reason companies have student-discount programs, often pretty aggressive ones, sometimes going all the way to basically giving the software away for free to students (Microsoft does the latter fairly often).
If nothing else, what students are familiar with affects the cost/benefit analyses of companies making decisions. If a lot more graduating students are familiar with technology X than Y, then a company will find it harder to hire for Y, and will pay more for the employees when they do, which pushes some companies to choose X. Obviously how much effect this has depends on a lot of factors, like how big and how persistent the imbalance is, how entrenched the industry standard is, etc.
Usability is a separate issue from deep color support, Pantone, etc. Any traditionally "religious" discussion (Gimp vs Photoshop, Vim vs Emacs, Win vs Lin, etc.) tends to be unproductive because both sides will make broad, sweeping, inaccurate, or unprovable statements, and when one side wins a point, the other side changes the subject, instead of people honestly comparing and contrasting.
...and to avoid further derailing the conversation, I'll stop here.
There are exceptions to most rules, including this one. Consider for example what has taken place with Blender. I know a lot of people who would have been learning 3DS Max (or Maya, etc.), but now know and use Blender instead because that's what they can afford.
And these students don't have to venture forth into The Industry. They can create their own that will topple the existing one. There are plenty of growing startups who would be more than happy to hire someone with "3D Skillz", and many of them don't care what tools they use, so long as the work gets done.