I go to Mesowest and I can get MSLP from any station, not just ASOS stations. And you can get it every couple minutes from all these stations including the ASOS stations whose's METAR only reports hourly.
Not sure what you are referring to with, "most PWS don't have this ability," in reference to calculating SLP. Just about any station I see reports SLP. In fact it is Altimeter that none other than the Davis Vue can calculate. So they all do SLP. But what the console does is irrelevant because every online service asks for stations to send SLP. It is only CWOP that asks for Altimeter. And any software that sends to CWOP has been designed to take station pressure and calculate Altimeter for use in CWOP only.
For consoles to keep track of the last 12 hours temperature is no big deal. The user does not need to know all that the station is doing to properly calculate SLP.
From what I've read probably many years ago stations were not able to do this SLP calculation and that is why CWOP being probably the oldest online weather service for PWS decided that Altimeter was the way to go because it was a simple way for most people to consistently and uniformly report pressure with that eras equipment. So CWOP uses Altimeter only because of legacy procedural circumstances. I got this information from the CWOP manual.
I'm not advocating SLP instead of Altimeter. I'm advocating for for both. I send SLP to everywhere except to CWOP where I send Altimeter. I can compare my station to other stations and I have data with both SLP and Altimeter. If I want to compare my station to the local media, no problem, I pull out my CWOP data. If I want to compare to other WU stations I know that I'm using SLP like the rest of them.