I think you mean, it's possible but almost never occurs in practice (or, due to the astronomical size of 2^160, theoretically, either).
Well sure, in terms of actual probabilities we will never see an address collision. But it is theoretically possible with a mixture of compressed and uncompressed keys.
Are these similar privatekeys have certain distances from each other? or they are random in the whole range?
I think what he is asking is if private keys which would give us an address collision are similar or located a fixed distance apart. The answer to this is no, they would be randomly distributed throughout the whole range.