Web Hosting Competition and "Soft Limits"
Many, many web hosts these days offer hosting packages with so-called soft limits. The effective opposite of offering "unlimited" things in hard-limited areas, soft limits are limits on services such as domain names, email addresses, and databases which cost the web host no extra money to offer. Email addresses, extra domain names and databases as the absolute best examples.
A web host offering 500mb of space, and 10GB bandwidth seems reasonable, until you look and realize that they only allow you to use one domain name, or only give you access to one MySQL database, or worst, they only allow you to use 2 email addresses. These limits are almost always incentives to purchase a more expensive plan, however, the experienced Internet-user will realize that with the high level of competition in the web hosting market, buying a more expensive plan is usually a bad idea. There will always be alternative companies around which can match what your hosting provider is offering, without the soft limits.
Remember: in the web hosting market, you as the client have the choice. With 1 of you, for every 20 hosting providers, you should be very picky in who you trust with your business and only go with the one whom offers the best service. While soft limits aren't inherently bad, they're definitely unneeded in the industry we are in. So how do you avoid a host that is limiting you in unnecessary ways?
Think about whether providing an added amount of a service would cost the host more money - if it wouldn't, they're probably using it simply as incentive to make you spend more money: go look elsewhere for better deals.