Why Nocster is able to provide 300GB/mth bandwidth with a package that costs less than $100/mth WHILE other companies charge a high price (for example, rackspace charges $715/mth for 300Gb/mth and Alabanza charges about $1250 for the same amount).

Is there a catch OR is there a difference of the type of bandwidth they offer?

I might be wrong in this, but most of these "cheap bandwith" offers are of the following reason(s):
1. They are way overselling their bandwith. For example, they are trying to sell OC3 bandwith at DS3 capacity
2. As good as their incoming bandwith may show up (from traceroute), they are pushing most of their outgoing bandwith through cogent, which is really cheap (about 10 cents per GB).

Not sure about Nocster, but I do think Nocster might do both of the above.

regards,
-dave