Huh? I'm not really sure what you are describing. I have around 8 bikes (none single speed) and when I pedal, the bike moves. If you are saying that something is slipping, then yes, there might be a problem. Like if the chain skips a few teeth upon initial application of torque, then yeah, your chain and/or cassette might be worn down to the point of slippage.
Try riding up a steep hill in a high gear (really mash it) and see if the chain skips a lot there. That will really show up slippage.
Seems like to me that you are describing a non-issue if chain slippage isn't occurring.
You also have to remember there is a ratcheting mechanism in the freehub so engagement of anything could be delayed a tiny bit because the rear wheel isn't fixed to the cassette itself.