Usually bandwidth depends on the datacenter. I believe some of these new companies see "unmetered" bandwidth go for it and do not realize you can max out still on unmetered bandwidth to where every single client is receiving slow speeds. So you will see ridiculous offers like $15/Month unlimited bandwidth which is not the same thing as unmetered, it just means you have a 10-20mbit line capped. Now the reason for a company offering 100 GB bandwidth compared to another offering 400 GB bandwidth is that each and every host is different aside from the sub companies of larger hosts, the same people take the calls as the main company. Most hosts are all at different datacenters with different prices on different amounts of bandwidth. Some datacenters get deals on bandwidth for being long standing customers, just like hosts will get breaks on prices for being a long standing customer with some datacenters. In the end the companies that oversell will hurt all their customers once it hits the fan. What they are concerned with is profit, the unlimited hosts want profit fast so they oversell dramatically not knowing that one customer with a couple high traffic sites that should be on a dedicated server can eat up all their bandwidth.