Who says it involves "phoning home"? You can use offline apps, and turn off your internet if you want. I happen to like browser based MIDI apps, but then again, I write them, so if it is "phoning home" (which it usually isn't unless I want it to) it is often to localhost. :)

Your comment could be applied to typewriters. Do you prefer the days when, if you wanted to write a book or article or something, you used a typewriter that was completely standalone? I kinda like having my "typewriter-style keyboard" connected to a computer... it opens up a ridiculous number of possibilities that you can't do with a standalone machine without a big display and a fast processor and a big hard drive. And maybe internet.... you can't exactly have Hacker News with a standalone typewriter, but you can with a keyboard that connects to a computer.

Same with a "piano-style keyboard."