Originally Posted by msu2001la

Agree. For top-level pro riders who are looking for marginal aero gains, internal cable routing (or things like aero valve stems) might make a tiny bit of difference so they're willing to put up with the annoyances that come with it, but for everyone else it's entirely aesthetic. Bike manufacturers produce most bikes with internal cable routing because people want/expect high end road race bikes to look like what the pros ride, and by extension it's an easy marketing win to make less expensive road bikes look like the higher end ones. Internal cable routing really doesn't add any cost to the bike and can be marketed as an "upgrade".

An aero valve stem is silly but if pros all start running it, it's a pretty good bet that you'll see it start showing up on road bikes at your local club ride or LBS.