I've just seen this. The letter only applies to SPL games. 125,000 people came to Fir Park last season for SPL, League Cup and Scottish Cup games. They paid an average of £15 each making £1,875,000. Rangers absence in the SPL would have reduced the total coming to Fir Park last season to 115,000. That might have cut gate income by say £200,000 or 8.5% or so. On 6 June we were told that season ticket sales were up by over 26%. According to the way you do your figures less than 300 Motherwell fans on average pay at the gate. Apparently we can look forward to much bigger home crowds without Rangers.
By the way, you're wrong about Hearts and Hibs. There were 7,456 fans at the last day of the season match agains Dundee United. I can't remember how many Arabs were there but it was at least a couple of thousand. In a more competitive SPL, without Rangers and with Celtic having to live without their greedy lion's share of resources, I believe attendances can only go up.