Jay, ULX v1 had 'flags' you could give each user individually.
Each flag had different means. Example, A might mean rcon access, B might mean gimp access
<user> <flags>
We believed when we went from v1 to v2 that the way we do it now would allow for not only more customization, but no limit to the number of access levels.
"ulx this" "ulx that" "ULib custom script this" "ULib custom script that"
26 letters fills up pretty fast with not much room for custom scripts written by those not in Team Ulysses
As for blackhawk's suggestion, Jay is correct. Other than 'guest(ulx user), admin and superadmin', in that order, there is no hierarchy inherent in Gmod, and ULib allows for so many more ways to set access that it would be difficult to have a 'increase' command.
We'd have no way of knowing which level was higher than another. Currently, my 'superadmin' might be different than someone elses, should I decide to edit the defaults.
ULX wouldn't be able to know this. Though we could write in code/levels similiar to Spbogie's UTeam, and Jay's APromotion, our current support is often times challenging enough without adding in additional 'make sure you're numbers are in order'.