Imperial Guard is by necessity supported by the Navy, since otherwise they can't even get to the fight. The entire reason Space Marines have their own ships is because they go off and take care of business without needing to involve the sluggish juggernaut of the Munitorum.
As far as Epic goes, as Simulated Knave said the Naval assets are the only way in which Guard can have any air support at all. The fact that Space Marine lists are 50% more likely to take Titans than Guard tells us three things:
1) All armies have need of durable ground formations,
2) Imperial Guard has access to decently durable formations,
2) Space Marine ground formations are significantly inefficient compared to the Warhound.
The first is an intrinsic part of the game. The second says that the Guard has a decent balance between organic and allied formations. The third point is where this conversation arises.

In order to make Warhounds less of an obvious choice (and lower their percentage of inclusion) either the Titan needs to become less efficient, or Marine ground formations need to become more efficient. I think the best plan is to split the difference somewhat. Since the Warhound is currently the most efficient option, lowering it directly will unnecessary penalize the list as a whole. Increasing sub-optimal choices doesn't increase the power of the list, it just makes Warhounds stand out less amongst their competition.
There is an argument to be had that simply increasing points doesn't necessarily change much, if the adjusted price is still worth paying. Likewise, decreasing the cost of sub-optimal choices doesn't necessarily make them better choices, it just means you might be able to squeeze in another activation. The current unit that I think most suffers from this is Tactical Marines. Fluff-wise, they should be the most present unit in the majority of armies, as a Codex chapter has 440 Tactical Marines in it (not counting any 1st Company Veterans that would be represented as Tacs in Epic) and yet it's rare for there to be more than 1 formation of them.
I just checked the Epic-UK tournament stats for this year and 2010:
Of the 15 Codex Marine lists that
placed in the top 5,
100% took at least 1 Thunderhawk, and 73% took two
100% took
at least 2 Warhounds, with one list taking three.
13% took more than a single Tactical formation