Yes, almost certainly. Only TVs released in the last few months have the ability to receive HD signals - but note that so far only 50% of the population are covered by HD anyway. Unless you've bought a TV recently, it's not going to have the required tuner for HD.
You have an HD Ready TV, technically - the "HD Ready" logo means a TV can display HD pictures from an external source. The "HDTV" logo means that a TV includes a tuner for HD as well.