Please check out this link as a start. You need to know a little more about tier-1 carriers. »
en.wikipedia.org/wiki/Ti ··· _networkHere's a list of large Tier-2 carriers. Note the second paragraph of the text. »
en.wikipedia.org/wiki/Ti ··· _networkGoogle is not on this list, although that does not mean it is not tier-2.
A tier-2 purchases transit from a tier-1, not the other way. Tier-3 typically purchases transit from a tier-2.
Purchase cost includes bandwidth. If you have a skinny pipe because that's all you're willing to pay, peak time access will suffer.
Comcast is a tier-2 ISP. Get a traceroute from a comcast address to youtube to see who provides transit.
From my VZ address, traceroute to youtube goes through Verizon through alter.net to the google gateway. While alter.net is a verizon business component, there's lots of folks who know VZ's right hand doesn't know what its left hand is doing.
You may find a traceroute to youtube from home a bit different than one from work. You can't tell if the hop is on a fat pipe or a skinny pipe, but I'll bet if a hop is showing packet loss and lag, it's a skinny pipe or it has a lot of traffic going through it.
I believe the recent FiOS slowdowns are almost certainly the result of rapid expansion into Quantum tiers. That's the single most recent event with the largest impact on network congestion. As FiOS subscribers continue to complain about network congestion, it will get addressed. Changes to a tier-1 network are never quickly made. Someone has already said it will take about 3 or 4 months for the network to settle down, same as it did when FiOS pushed the envelope with the new high-speed tiers back in 2010 and several times since then.
One really interesting problem is how google's gigabit fiber in Kansas City will transit to the internet.