Except none of them NEED your support. ...no other class will have a harder time finding a chance to use it's at-wills and make em work to full strength than the Warlord.
If you're playing a Warlord, you NEED at least one other PC to be very actively positioning themselves in regard to your powers. Probably more than one if you want your encounter and daily powers to have their full, mathematically expected benefit on the encounter.
In order for Wolf Pack Tactics to be worth anything there HAS to be an ally who wants to shift one square...
...for Commander's Strike, Viper's Strike, and Furious Smash. Another character HAS to be ADJACENT to the Warlord and/or his target.
The cleric needs an ally somewhere in the battle for his powers to get their full effect, a reasonable condition for a leader. The Warlord needs an ally somewhere they won't be most the time. Where they can't be much of the time even if they are trying to work with him.
There may even be a friendly helpful player who knows how all your powers work but there just isn't any good the power could in that situation.
And I'd like to point out that this dissatisfaction with the Warlord and his at-will powers has nothing to with him being a "support" class.
The way to make Commander's Strike a better power would be to give it a range of 5. This wouldn't increase Commander's Strike's mathematical effect on the battle, but it would greatly increase it's ease of use.
So in short, it's not so much that the Warlords powers are mathematically weaker than the Cleric's or other classes' powers, but that they are SO much harder to find a chance to use. Mostly because of their limited range and awkward requirements that an ally be positioned just right.
Heck, I bet the game assumes that a successful Furious Smash will always be followed up by an attack from an ally. I think it was James Wyatt who said the game assumes the Rogue has Combat Advantage every turn for him to keep up in damage dealing with the Ranger. The Warlord has a similar problem compared to the Cleric, only much, much worse. The Warlord just can't possibly use his powers well as often as the Game Balance God's assume he can.