High battery use when idle

For those of you who aren't too familiar with english slang, a forthnight is 14 days.

On to the question : Normally it takes about a week to 14 days for battery use to drop to a normal level, so by now yours should be at full capacity. 
Mine loses 4-5% overnight (8 to 9 hours of sleep) while being on regular standby.  No WiFi, no data, no airplane mode.  Just plain standby.

Your posted values are pretty normal as well, so it doesn't look like there's an app running in the background and draining the battery. 
I'd think that your battery simply doesn't have decent capacity.

(DISCLAIMER : I'm no technician and can't make a 100% correct diagnosis based on your info, I'm merely using my past experiences, logic and common sense)

I'd suggest that you make precise notes (percentages of battery use, how much you call, browse, it's effect on battery percentage, etc), take it to the shop and ask them to have a look at it.  If possible, ask to talk to someone who knows Android.  Maybe that person can dig into it, find a software problem after all and solve it on the spot.

Nothing unusual about those values.  I wouldn't worry about them.  As for them being so high, cell standby and phone idle are the result of the energy the phone needs to send and receive signals.
While they may be high compared to most phones, it's slightly disproportional because Android itself barely uses any energy.

Keep in mind that the Desire HD is one of the most powerfull smartphones available, but has a very low-capacity battery compared to it's rivals.  So these figures actually aren't bad at all.  Android is by far the most battery-friendly smartphone OS I've seen.

The Android OS evidently learns your usage and so battery life will improve over the first couple of weeks of usage, mine certainly did.  So give it a little bit of time and see how it goes.