It's 50% because there are OTHER costs involved, including operation of the club, rent payments, revenue sharing, paying employees, scouts, etc., and $11M in health and medical benefits(which IS included in the luxury tax calculation). That's why it's close to $115-$120M, which the O's cannot sustain without a huge boost in attendance, more favorable terms with MASN and/or a deep World Series run. And the numbers for payroll came from Cot's.
And while the team can't close the window of contention, other bigger markets teams like the Yankees can by stealing their free agents for more money than the O's can afford.
Oh, and here's some food for thought for you:
http://www.baseball-reference.com/teams/BAL/2014-payroll-salaries.shtml
Including estimated arb raises (which will likely be MUCH higher than the measurements Baseball-Reference has at $74.5M, which won't be even close), Baltimore will likely be over $90M-100M, with little room to resign their free agents.