In American law, a covenant is best thought of as something different than a contract. They are related, but covenants are a property law concept, while contracts are their own area of law. A covenant can run with the land: someone in 1920 can put a restriction in a covenant that the owner of the property in 2014 must abide by, even if the property has changed hands many times in the interim. However, contracts only bind the parties that agree to it.
The distinction between the two is very relevant vis-a-vis your response to 'tptacek. The terms of a lease contract are freely bargained-for between buyer and seller in the present day. Because contracts cannot bind non-parties, they will only contain provisions that at least one party considers meaningful. However, a covenant is not freely bargained-for between buyer and seller in the present day. Both the buyer and seller may be bound by provisions that both believe to be antiquated (like covenants not to sell to particular minority groups).
If you think a contractual term is antiquated, you're free to bargain with the seller to have it eliminated. With a covenant provision, however, both you and the seller might be stuck with what someone wrote-in decades ago.
http://en.wikipedia.org/wiki/Deed_restriction