Please don't make stuff up.. The Nexus 7 will draw the same amount of current off the charger if it's asleep or awake. The amount of charge going into the battery will of course vary based on how much power the tablet is drawing.
It may exceed that of the charger, therefore continuing to drain the battery. But in more typical cases where the backlight isn't at 100% and the CPU isn't at 100%, it should still charge just fine.
There is something inherently wrong with the N7's charging, it's very very picky, but being asleep has nothing to do with it.
Who is making stuff up? Have you tried plugging it into any sort of meter or do you have a wealth of N7's that you've tested with? I won't deny the N7 has hardware issues, but this is always the way it charged.
Use a 3ft 24AWG cable. When you first plug an N7 in it stays at a lower draw as long as its being used.
Once the device goes to sleep, give it time and the draw will almost double. Did it this way on the OEM build and the cyanogenmod build.
After it upgraded to 4.4 I had to reseat the battery before it would behave correctly again; it wouldn't charge even at the half rate I mentioned.
All of this was using a dedicated charging 24AWG cable from ebay, or a monoprice cable shorted out.