The Steelers could have easily invested in an offensive line this year and put off resigning him till after this coming season. That way the whole no offensive-line excuse would be out and they could get a better idea of his worth. He did still have two years on his rookie contract afterall. Also another year most likely would not have really jacked the numbers up much as the deals he is being compared to were done in prevous years with no real comparable ones for comparison coming up in the next year (Romo and Palmer are of similar experience/age whereas Manning/Brady obviously have rather long proven resumes).
Also the Steelers should have included a clause saying if the jackass got injured/killed riding a motorcyle without a helmet any/all funds received under the contract would be forfeited back to the team.