A draft-cross is a cheap-man's warmblood. I love my draft cross and I call her a "rudimentary warmblood." To sum up Spyder's eloquent and very correct explaination: A long, long time ago, people wanted athletic (hot-blooded) horses to be bigger, so they bred in "big blood," basically your draft horses. Then they bred the better ones together and developed breeds and eventually registries.
I'm a poor college student so I bought a draft cross, but beware, a draft cross is much lazier and heavier than a warmblood.