I would say that it's a combination of both. I personally don't automatically assume the delay when clicking a link is due to the number of abstractions between

I would say that it's a combination of both. I personally don't automatically assume the delay when clicking a link is due to the number of abstractions between my mouse and the server-side hardware that a website is running on. In the YouTube example, you have very real speed-of-light constraints. I fired up the Chrome debugger and loaded the main site. I had over 100 requests in the first couple of seconds. Even with a very low-latency connection, assuming that your browser can "batch" the requests together, and instantaneous server response there still is an overhead of request/response of at least tens of milliseconds for each request (or group of requests). To reduce that time, it requires reducing the number of requests, assuming that javascript/images are already loaded, parallelizing or delaying the loading of "ancillary data" etc. All of which have nothing to do with the speed of the server or the client.