Some of the excuses are just pathetic. If the job is such a toll on family life and health, etc, why not stand down now? Who else gives a year's notice? You can bet their constituents will be getting a less-than-stellar service ("What you going to do? Sack me?"). As anyone who has worked out a notice period can attest, their hearts will not be in the job.
But their fingers may very well be in the till: once you've stood down, what's to stop you gorging on the as-yet-unreformed expenses system? I would not be surprised if the number of voodoo MPs doubles in the next few weeks. So, we have a desperate government which already has less popular support than any in postwar history. And now the majority of MPs will go at the next election. The case for an autumn election grows stronger with each resignation.