In the Nineties, they'd have very probably been using a wet printing minilab - when they were set up well, and properly calibrated to the film that was being processed they were good. When they were a little out of adjustment, the chemicals were on their way out, or if you took in a film that wasn't in the operators repetoire when it came to processing settings (for which read colouur corrections) then they could be horrible. I've entire boxes of family photo's where they were a fetching shade of magenta straight from the processing labs (my mother insisted on using Truprint, as you got a "free" film with the processing, despite the HORRIBLE quality of the actual processing)
I think that most modern minilab setups do a hybrid approach - develop the film, then scan it and print the photo's using either inkjet or dyesub technology. This at least opens the door for you to get a CD of the images at the same time as your prints, and also allows the machine/operator to do a little colour correction if needed. I know for example, before I started processing/scanning my own C41 film I took a roll of XP2 to my local boots, and mentioned to the operator that it was a Chromagenic Black and White film, so not to be surprised if the prints were a little "iffy" - He just said "Ahhh XP2, i've got a setting for that on the machine... Would you like Black and White or Sepia toned prints?"
As an aside, I've also scanned the negatives of some of the horrible magenta shots mentioned above, and with a little time and the odd tweak in CS5, I've been able to rescue pretty much all of them!
I'd be surprised if Boots are using old machines, or running them on expired chemicals, they've always tended to go for the upper end of the high street processing market (though as with anything - it does depend on the person operating the kit). So I'd expect their machines to be working well. Comparing a well calibrated and operated wet minilab from the 90's with a modern hybrid minilab, I'd expect that the differences would be negligeable to be honest - certainly on 6"x4" prints.