I don't think that's the deal breaker for experienced players. That'd be pretty to solve with a bluetooth foot-pedal. Here are a few of the things that come to mind that pro-level folks would have hang-ups on:

• Typesetting: I don't know what score format they're using, but this can be a big one. There's a big difference between a professionally engraved score and just having the right notes there.

• Annotations: From the conductor, self, whoever.

• Overview: Professionals scan a score looking for key parts. This seems virtually impossible in iPhone format, but would be workable on the iPad.

• Size: Even the iPad is small compared to a performance sheet music page.

I suspect the three big market segments are hobbyists, children and church musicians. There are relatively few professional performers.