The prices are calculated by taking the volume-weighted average of each exchange price listed on the coin's respective overview page.
This calculation will likely change in the near future. An exponential moving average may prove to be more useful.
Most of the advertisements on other sites are for blatantly fraudulent ICOs aiming to take advantage of people that are new to cryptocurrencies.
Aside from that, ads are extremely annoying on sites like this, especially when you are on a mobile device.
I do not need any advertising revenue as long as the price of BTC continues to increase over the long term!