The author of that page has a small section concerning rates in the Chicagoland area. There are many possible reasons for this. Some are faster than others from a hardware perspective. Some sites are very graphic intensive. This causes longer load times for pages from their site.
Some sites are just more popular than others.
Standing in line to get a table at a popular restaurant is exactly the same concept that applies here. These are the heavy hitters to remember when your session gets slow. Try coming back to these sites at a later time, and they might be less congested. Install the program. This is where you want to put all of your files.