Short answer - yes. If an employer wants to take a chance that an employee won't go to tribunal then they can do whatever they like.
Longer answer - Is it just your opinion that its not gross misconduct, have you checked your company disciplinary policy to make sure? most companies slip something fairly trivial in there to give them an out if they have someone they want rid of but who never does anything bad enough to get sacked for.
Most companies will have breach of their internet or email policy listed as gross misconduct - because everyone breaches those 2 policies all the time it's an easy out.
However - if what's happened isn't listed in the policies and is trivial, then it would depend on previous employment and disciplinary history. In my experience if a company wants rid of you they generally can find a way to do it.
Just like everything else, Employment law is mostly opinion (apart from wages, taxes holidays etc.) if a company thinks you won't take them to a tribunal they can do what they want and potentially get away with it.