Not that any of the MSN applications are particularly large (averaging less than 10MB), so it's not clear why anyone would want to put these on card (risking losing the apps if you take out the card later), but I guess it was an implementation omission that needed fixing at some stage by Microsoft. And, doubtless, there were minor bugs fixed to each application that haven't been worth mentioning in a changelog.
Quick links to the various MSN applications, in case you're missing one(!):
PS. Bonus tip (because I keep forgetting myself!) Before removing a microSD card from a Windows Phone, always go into Settings/Storage Sense/SD card first, swipe to the bottom and tap on 'remove SD card'. Failing to do this means risking data loss or corruption, since the OS will almost certainly have some files open on the card at all times.