"contention ratio of up to 25"
No, try 50-1. dialup was about 25-1 to 30-1.
For web browsing and email, dialup meant it took about the same amount of time to download a large page as it took to read it (unless it was mostly text). People often read the page as it was downloading. So your modem was on full-speed nearer half the time.
At broadband speed, you didn't read 120x faster but your data could get through 120x faster, so your connection was idle for these low bandwidth tasks most of the time, so (despite telling you you could download movies, play games and so on [all of which took longer to download than view]) they upped the contention ratio.
After all, since your ISP pays for the size of the connection, rather than the amount of data passed, any unused bandwidth is a lost opportunity to get another paying customer to use it.
So, when people started using YouTube and other media sites, they had oversubscribed because they'd hoped nobody would be going back to the connection profiles they had under dialup. Rather than pay the frankly piddling cost of halving the contention ratio, they decide to throttle your connection.
I've apparently got a 2Mbps connection. I have checked available connection speed on many occasions and I generally (~95% of the time) see less than 1Mbps. Once on Sunday I saw 1.5Mbps.
NOTE: an OC3 with 155Mbps connection costs about £2500 a month. 50 people at 8megs is a couple of quid a month (about £2.50).