Michael:
Just judging from the behavior I saw when messing around with the Mail.app, the LSBundleIdentifier can have only one value at a time and there can only be one for the type "U:mailto". Basically, it records whatever the user has selected for use as their defauler mailer, not the mail capable apps they have on the machine.
Actually this -> kLSAcceptDefault <- might mean more or less what you're saying. I haven't tested this for some time, I may never have verified it ever returns multiples, at least the URL part. I'll test that.
