Michael Martin is an awful Speaker, his 2001 election was tainted as it emerged that Labour MPs placed bets on his election since then he has been partisan and inept and his attacks on Kate Hoey and Norman Baker have robbed him of any credibility he might have had.
Having said that isn't the rush to kick him out a bit of a smokescreen?
Whilst he does formally oversee the Fees Office which approved all the claims, it isn't as if he created the system or could simply annouce great changes to the expenses process. The system existed pretty much in it's current form even under the sainted Lady Boothroyd and other competent Speakers. Those claims that were outside the rules, such as for mortgages that had already been paid, cannot be blamed on anyone but the MPs themselves.
Getting rid of a sitting Speaker runs the risk of politicising the role even further if his support is spread down paty lines. It also risks making him a scapegoat for the avarice of other MPs who can kill the expenses story by offering up high profile sacrifice.