I seem to have a vague recollection that the Freedom of Information Act was cited in order to get public disclosure of MPs expenses. The woman who, I believe, brought it via judicial review, was an American woman who was a journalist and was very passionate about public accountability. One of the defences was MPs having their personal details in the public domain such as addresses. I seem to remember that she faced such opposition in terms of making it a right to have this in the public domain. Wonder why Don't seem to remember the Telegraph rushing to her defence at the time?
In general terms, the factor that has been missing has been the public scrutiny. Sure, no rules have been broken, but isn't it incredible that MPs, with no change to the rules, are writing checks left, right and center to pay back the taxpayer. So, it's the cheeky little schoolboy (and let's face it, Westminster is an old boys network) trying it on, and getting hauled into the Principal's office for a telling off!
I think that MPs need to have a certain amount of discretion, and that extends to expenses. Either we trust these people, or we don't.
By the same token, now that they will know that every receipt will be under the microscope, I think that's a huge kick up the ass, and hopefully that's all that will be needed.