I don't think the cost of implementation is a particularly relevant factor in a decision about whether or not to comply with the law, but the size and likelihood of any fine for not doing so might be.Where you are investment has probably been made in the software and hardware that makes it possible to implement those kind of changes for a marginal cost.
I don't think the law makes any distinction - the required standards are the same. We might debate the degree of success of certain elements of the user interfaces, but nobody can dispute that fact that some TOCs like LNER and Northern are making genuine efforts to comply. It's the TOCs that have done nothing beyond putting inaccurate disclaimers onto their machines that are the problem.IMO ticket machines should be held to the same standards as face-to-face sales.