if burglary carries a sentence of Y, should someone who steals one item of jewellery from each of X houses get an X times greater sentence than someone who steals X items of jewellery from one house?
Yes, otherwise you end up with a formula for sentencing based on the value of the items stolen, which means that you're showing that all you care about is property. For an awful lot of people who are burgled (possibly the majority?) the main hurt is not the loss of property, it is the feelings of violation and insecurity, so if you burgle X houses you have put X x as many people through that as if you burgle one.
If the penalty for speeding is a fine of Y and 3 penalty points, should someone who drives at 85mph along a fairly short stretch of M25, passing X speed cameras as (s)he does, get a fine of X*Y and 3*X penalty points, whereas someone driving at 85mph for the same distance along a road that has only one speed camera in that strench, the penalty is just Y plus 3 points?
Once you start down the path of saying that people should not be punished for a wrongdoing because others were lucky not to get caught doing the same thing, where do you stop? Do you bring all police forces down to the level of the worst performing one, for example? If Newtown has a particularly talented CID, but neighbouring Marketown has a bunch of no-hopers, should Newtown have to let go without charge some of the people it catches because Marketown would not have caught them?
With your example, there probably are (should be) guidelines on how far apart camera detections have to be to count as separate offences, but your example could be replayed as someone getting caught by a mobile police radar control, pulled over, processed, and sent on his way, and then a few miles down the road, speeding again, getting zapped by a Gatso.
It might be oppressive if they put, say, 4 cameras on a 200m stretch of road and end up disqualifying people for what could be regarded as one offence, but in general, as long as the spacing between cameras is such that it's reasonable to regard the detections as separate offences, I've got little sympathy for the argument "I should be let off because other people don't get caught".