I think they are only different because of the segmenting of the market. There aren't too many 'senior managers' (whatever one interprets that to mean) in an organisation, and part of the benefit of training is cross-fertilisation of ideas from others - so such training organisations promote 'senior mgt courses' in this and that as a way of trying to ensure the participants are reasonably balanced in terms of knowledge of mgt theories, previous experience and ability to contribute. Part of training across organisations is networking opportunities too. If its about enhancing a skill, say 'leadership' people are generally more comfortable making mistakes (whilst learning) in front of their peers rather than in front of 'juniors'. When I organised training, I would never put people on a general course across more than 3 levels (grades) of management/supervision - it just doesn't work. More recently running training for a public sector org, if I am asked to run something for grades Cs and Ds and some E1s get in on the act, they normally sit there for a couple days and say nothing, however much one tries to bring them in. They are just out of their depth intellectually. But run a course for E1s only and it works.
Hence that is how I think there is a market for public, open, senior management courses. I don't think the methods are any different - just the best facilitators/trainers who are good at what they do - oh, and better catering!