"Is there anything you can do on an ipad that you cannot do on a surface?"
Well, there are at least 450,000 or so apps that you can run on an iPad that you can't run on a Surface. Among the apps that overlap between the two devices, some aren't as fully featured on Surface and some cost money while the iOS versions are free. You have LTE options with iPads that you don't have with any Surface but the Surface 2. iPads can sync with Macs in useful ways that Surfaces can't--e.g. Continuity. iPads are the only tablets that run iOS 8, which is a subjective distinction, but you're simply trolling if you think that just because you prefer the Modern UI, everyone must prefer the Modern UI.
In any case, I could keep going, but I think I've made my point: There's plenty that you can do on an iPad that you can't do on a Surface. You might not care about the distinctions-- but that's about your needs. Again, it's trolling to define devices purely in terms of what you think is important. All I said is that the Surface Pro 3 has uses that are mostly centered around its laptop mode and the pen, while iPads have a different set of uses. They're both excellent devices for certain needs. It just makes increasingly less sense for us to keep comparing them.