Comment Err, no (Score 1) 135
If you take the time to analyse a modern page, you'll see that the ads usually represent a relatively small chunk.
What really slows the pages down is over reliance on javascript frameworks. Pages that use both jquery and another framework such as scriptaculous are not uncommon. What's worse is that the developers often use these libraries for trivial effects, stuff that can easily done directly in javascript. Then most pages have scripts for at least 3-4 social media sites (Facebook Like box, Twitter counter, G+ counter, etc.), live tweet box, 5-8 different css files...
And then they spend a fortune on bandwidth, CDN services and faster servers, when by optimizing content they'd get more performance.