Many OSC based applications for the monome[1] were ported to work with the copy-paste-avalanche of grid controllers (Launchpad, APC). The USB-MIDI data rate limitations are clearly visible when trying to change the state of 64 keypads at once. 64 individual signals with 8ms latency completely break the flow[2], compared to a single optimized OSC message.
Your counterpoints are correct, but MIDI is a better choice over OSC only due it's widespread compatibility. However, it's pointless to stick to USB-MIDI in the long run. It couldn't support the more complex DIY controller requirements as far as 6 years ago, so I can only imagine the chasm increasing.
A new inter-operable standard that surpasses MIDI and OSC was envisioned back on 2009 called ioFlow[3], but unfortunately it hasn't taken off yet.
P.s.: The website the story refers to is returning a 403, so my comment is here only to support the claim, that starting out with MIDI in 2013 is not the best idea.
Edit: Now that the site is online, I can respond to the product itself. It's probably a good fit for keyboard musicians, but I'd recommend the true hacker to pick up this indy marvel: Madrona SoundPlane-A[4], which has been in development for approximately 4 years. The concept is very, very similar. But it's not bound to the linear piano scale like the Roli. You can play it like guitar frets or better yet, explore 2 dimensional note layouts, such as the ones invented by Euler[5], popularized by Kaosscilator and now Ableton Push. Also, it runs on OSC, so you can enjoy the low latency, and build your own paradigms by transforming the signals in Cycling 74 Max or other OSC capable programming environments.
[1] http://monome.org/
[2] http://en.wikipedia.org/wiki/Flow_(psychology)
[3] http://ioflow.berlios.de/
[4] http://madronalabs.com/hardware
[5] http://en.wikipedia.org/wiki/Tonnetz