Somehow I and a lot of other people missed the news about TB2 when new mbp was introduced. Maybe because there weren't drivers at that time to use 4k @60Hz. I just thought than newMP was first with TB2...
It's still really hit and miss in terms of what works at 60hz. I think anandtech had an article on that about the lack of standard specifications for MST. I don't think Apple would intentionally hold back the macbook pro. It sells many more units than the mac pro while retaining a strong ASP.