The way the contracts have previously worked (and it's been years since I purchased a directv receiver)
When Directv covers some of the cost of the hardware there is a contract. If the receivers didn't carry a directv discount you had to pay full retail price. Direct historically hasn't given discounts on HDTV receivers. That may have changed, but if you pay more than $500 or so you shouldn't be forced to sign up for anything, you are carrying the full cost yourself.
To add to that, it doesn't come with a dish, so it's not a "ready to use" system. I don't think you'll be tied down. But just read all paperwork you get at the store and don't sign a service contract.
Like I said before it's been a while, but as far as I know the policy hasn't changed.