Speculating based on what we've seen or heard, I would think that heavy armor is actually going to have to offer more in 4th edition than it did in 3rd edition to be used.
In 3rd edition, heavy armor offers 1 point of AC potential versus other standard armors, but it is a lot easier to reach that potential, so in most situations, the net gain is three points of AC, a few stat points (that don't need to go into dex) and a significant portion of gold (that doesn't need to go into enhancing dex). In return for that, the heavy armor wearer has to take a movement penalty that only sometimes works out to be significant (and which can be somewhat made up for by using mithral fullplate with a barbarian level or dragoncraft fullplate with a barbarian level) and some penalties to skills that they generally don't use.
In 4th edition, OTOH, it looks like the armor class delta is likely to be smaller if you can't add your dex to AC in heavy armor and, while the speed difference will be smaller (5 to 6 instead of 4 to 6), the inability to add dex/int to the reflex defense sounds HUGE. (Imagine how many people would wear heavy armor in 3.x if it penalized your reflex save--I'm thinking you'd probably have at least 50% of the heavy armor users say that a point of AC is not worth the reflex penalty). Furthermore, heavy armor also seems to penalize both the skills that oppose grab (a feature seen on several of the previewed monsters and thus likely on a significant portion of the monsters in the game). Imagine if heavy armor imposed a penalty on your grapple check in 3.x as well as giving you a reflex save penalty.
For all that, it had better give a pretty significant AC boost or it won't be worth it.