Its coded in the firmware on the switch. There was a discussion about it a long time ago (I cant find the post), but I believe the main concern at the time was the lack of space on the device (firmware flash size). If you allow the minimum value to be set to anything up to 99, then you have to add additional checks/logic to ensure that the minimum value is not set higher than the maximum value.
The 500 series chipsets in these switches has very limited firmware space, and some features have already had to be removed to free up enough space for some of the enhancements added in the beta versions.