For those that say Tillman doesn't have anything left to learn at Triple-A, I don't agree. He was 11-7 with a 3.34 ERA last season at Norfolk - good but not dominant stats.
He is still not going to be 23 until April 15 and while he has already made 39 Triple-A starts over two seasons, he can still work on things like perfecting that cut fastball at the minors' highest level.
Should there be a need or injury in Baltimore, he is a phone call and short drive away. The way most teams have to deal with pitching injuries, if Tillman goes to Norfolk and throws well, there is almost sure to be a need for him in Baltimore and that could come sooner than later.
As for Britton, I have stated many times before that it makes good business sense for him to not join the Orioles before late May or June to avoid Super Two arbitration eligibility status and also gain another year before he hits free agency.
Also, remember, he has only pitched in 66 1/3 innings at the Triple-A level. As good as he is, he can still work some on that change-up and Mike Griffin, the Norfolk pitching coach, has said that Britton still needs work on his fastball command.
Tillman and Britton are right on the doorstep of the O's rotation. Making them earn it and stay a little longer in the minors is not a bad thing at all.