An awful lot of different types of rods have heavier actions and higher ratings than they did twenty to thirty years ago. Carp rods, barbel rods, poles and, yes, even "match" type float rods. With carp and barbel rods it's obvious due to the test curve ratings. It's less obvious with float rods due to the inconsistent way that they are rated. However, if you look at the general trend in line ratings, or casting weights, they've definitely crept up over the years. Another indicator is if you actually try to buy a modern equivalent of the old style light match rods, there are very few about. Drennan have given line ratings for years. Just look at their old match rods compared to their new ones. Despite the fact that they still do lighter float rods than much of the competition, their line ratings are quite a bit higher than the old stuff. Take the IM8 Super Waggler at 1.7-3.2lb mainlines, 10oz-2.4lb hooklength. The IM8 Specimen Float, 2-6lb mainlines. Team England Action Tip, 1.5-2.5lb mainline, 10oz-2lb hooklength. IM8 Super Crystalite, 1.7-2.6lb mainline, 6oz-1lb 8oz. Only the Crystalite was considered particularly light actioned back then. The out and out specimen float rod ratings look decidedly average compared to modern match rods. When you consider that the current light Drennan float rods are the Acolyte Ultra (2.5-4lb+ main, 1-3.5lb hook) and the Matchpro Ultralight (2.5-5lb main, 1-4lb hook), it definitely shows the relative increase over the years. Perhaps there was some element of them playing safer with ratings back then, but I wouldn't attribute the increases entirely to that. The average modern "match" float rod is rated to 6lb mainlines. Specimen or commercial float rods are likely to have ratings up to 8, or even 10lb mainlines.
When it comes to carp and barbel rods, a large part of the creep is down to the methods being used and the increase in leads/feeders being used. I'd also suggest that people expect to be able to cast further and further using those bigger leads. The bottom line is that increased test curve ratings in such rods has very little to do with the size of the fish concerned. It also gives no indication of the rod having a fast or through action. It's quite possible to get a through actioned rod with exactly the same test curve rating as a fast actioned rod. They'll feel quite different in use though. You can still extract decent barbel on a 1.25lb rod, or a damned good carp on a 1.75-2.25lb carp rod of old. However, you'd probably wreck them if you tried to cast too far or use the heavy leads/feeders/PVA bags that are commonly used now.
