You'll find the word "Demonstrated" ahead of them and find it's rare to have an actual crosswind limitation placed on the aircraft in the AFM.
The only commonly seen limitation has to do with the prohibition of landing with a tailwind component in excess of 10 knots.
The only time I've been limited in crosswind component was flying for a domestic 121 airline which placed a limitation in our SOPs which matched the demonstrated crosswind component for the aircraft (28kts). Because it was written into the GOM it became regulatory and as such had to be adhered to. The other AFMs on my shelf even go out of their way to specify that the demonstrated crosswind components are not limiting.
The Cessna 172 posesses no such limitation. It's been years but memory serves it was demonstrated to what...12 knots or so? Hardly a meaningful limitation for a high winged airplane with plenty of rudder to go around.
It was actuay demonstrated to 15kts, for the 172. that was a test pilot flying a new airplane with a new engine. obviously an old airplane(which a lot of clubs have) with a pilot that might onl fly 2 or 3 times a month, and mostly on calmer days, will not handle that limit as well.
i was talking about that limit with m CFI while we were working the crosswinds the other day. he had stated that the 172 tends to run out of rudder at the 15kts component.
as for it being a hard fast limit, i believe it is, but then who am i? i've only got 194 total time, and can deal with 8-12kts. 8 is a bit of a workout for me, 12 is difficult. by the end of this year, they'll be easy as i'm spanding all of my non-solo time with my cfi to nail the crosswind landings.
i've seen too many accidents(or near accidents) caused by them, and get the impression that too many pilots have trouble with the winds once they go over 5 or 6kts.
lastly, if you REALLY think you're man enough to land in 25-30kts crosswinds, and you rent(or own i think) go ahead and bend the airplane and find out how insurance deals with it. most of our local clubs also impose the 15kts component. there's a lot of dead and fubared pilots that think they were better than they are. this includes ATP pilots too.
maybe i'm a bit overly cautious, but there will never be an NTSB report generated due to my neglect, or taking an unnecessary risk. my favorite 172(the only one left now) in the club has tried twice. electrical system failure at night, and partial engine failure on take off......both came out great, and were both good learning experiences.