I don't automatically put two y starters on my staff, but as indicated somewhere above, it can happen depending on what best fits my team and stadium.
The SIM gives a 5% advantage in the opposite hand pitcher/hitter matchups, or so it's been said through the years. Most hitters are right handed. If I'm playing home games in a stadium that has + HR numbers to field then I'm more apt than not to avoid starting a y starter