Although many would claim Starcraft as being the king of RTS, I personally enjoyed Total Annihilation. To me, the wide variety of units at your disposal multiplied the potential strategies. Now, there were 3 frontiers to consider; land, sea and air. Dawn of War is mainly land, and that's fine.
I recall units that I rarely used. Some perhaps never, but its not that they weren't useful. They just didn't apply to the strategy I had in mind. The different units made it interesting as I would begin to use new strategies and steer away from those I would normally use all the time. Try something new. This prolonged my love for TA, and because I was spoiled with such a variety for units, I couldn't take Starcraft seriously. Although I'll admit, I preferred Starcraft's graphics. TA's graphics sucked.
Regarding DoW, what I am noticing is that the variety of strategies are quite limited. I'm still learning Eldar though and they seem to have more flexibility. More thinking involved as they don't have the muscle the Space Marines have.
Adding units alone won't satisfy the thirst though. Some "out of the box" ideas may need to come into play. In the mean time, I'm hoping to see more units added to the existing races, as well as new races be added. I'm watching all the mods carefully and they do look promising. You have to give credit to these talented people.
I hope to see Techmarines and Chaplains. Perhaps a variety in tanks. I love tanks. Those World War 1 style tanks are just fascinating to look at.
Slightly off subject, something that would be interesting for the game, or any RTS game, is some sort of Purchase Point system before the game starts.
For instance, as the game is being setup, you get "100" points. Perhaps req points or a seperate point system all together. Now, 100 is negotiable. With those points, you can decide what you want to "purchase" as starting units. That way, your strategy begins before the game does. You will start with the units that best implement your own personal strategy. Perhaps the points can be modified in the game option screen.
Just an idea to throw around. I'm trying to think outside of the box. Bring the best ideas out of everyone. Spark some synergy.