Given that the most common healing triggers are "per encounter" (being the leader heals), and given there isn't usually much incentive to not heal when one can, I don't see how there being an expected adventuring day length affects the use of healing surges - either you are damaged and you use them, or you aren't and you don't. I just don't see how a standard encounter length of day makes healers more effective.
Now for daily healing triggers, I can see that, but from my own experience those tend to be in the distinct minority and saved for when they are desperately needed, so its not like a longer day would make the party waste these - in either case they would be used when they need to be used.
After all, its not like a party that doesn't know if another wave of monsters is coming in are going to say "Don't heal Jonny - we might need that healing" - indeed, there is more incentive to heal him now if monster might be coming, as he's more likely to end up dead if you don't.
I can only speak from my own experience (and the postings of others that I vaguely remember), but:
If your party knows to expect say, 4 encounters each day, then they can easily budget their healing surges (divide by 4). They know that if they "save up" one from the first fight, they can use it in fight 2 or 3. They know how many encounter level heals the leaders have, and how many they will need to use as a second wind. They can plan on using healing surges after each fight but the last one, where they know that they will be able to take an extended rest.
All of that information and planning allows the party to use healing in the most optimal way in each encounter. They don't waste surges, and they don't waste daily heals.
If, on the other hand, there is more uncertainty, then the party can't always be assured of making the most optimal choice in each encounter. If they
think that there will be more encounters than there actually are, they may conserve healing or surges and play defensively when they actually could go on offense. If they guess wrong and there are more encounters than they are expecting, then they might find themselves short on surges or extra daily heals in the last fights.
Giving the players meta-game knowledge like "We always get 4 encounters and an extended rest" allows them to manage their resources more effectively, thus increasing the effectiveness of healing, even though all the healing powers are the same as before.
If Ranger Bob has one healing surge left, but knows that after this fight, he can safely take an extended rest, there's no reason NOT to use a Healing Word during the fight to keep his 'HP buffer' full. If, on the other hand, he might be able to take a rest, or might need to press on, he might want to save that surge, put away his bastard swords of doom, and hide behind a rock and shoot some arrows. This reduces his effectiveness in the fight, in order to allow him to participate in another fight more effectively. If there is another fight, that decision was probably wise. If there isn't, then he reduced his effectiveness in this one for no gain.
That's why, in my experience, an "expected adventuring day length", increases the efficacy of healing. (Note that I am assuming this is a rational expectation from the players, and not "I never had any idea that you might have more encounters, sneaky DM, even though you've done it twelve times before!")