I have heard this before, mainly from spokespeople of the insurance industry. If it really is the case that motor insurance is a loss maker why are they queuing up to sell me insurance policies on which they are losing money? They can not ALL be so desperate to go out of business.
It sounds like a sob story to justify exorbitant premiums. Further to that we are told that the premium is based on the actuaries calculation of risk based on previous experience. Really? If that were the case then pretty much all premiums for similar risks would all be within a spit of one another. We all know they vary by a massive margin.
The 2011 results are just out. The UK motor insurance market lost about £600m. Those figures came from a firm of consultants, using data which is available to anyone who cares to pay (surprisingly little) for it. Any hardness in rates in 2010 and 2011 is now vanishing.
As Cunobelin points out, they're surviving by cross-subsidy from other classes. No-one wants to withdraw from private motor (a) because it's a flagship product, (b) because it's filthily difficult to tell what the actual rate should be, alarmingly easy to get it wrong and absurdly easy to kid yourself that you're making money when you're losing money and (c) because the advent of aggregators means that the game has changed and no-one really understands it at the moment - and it's easy to assume that you do.
Based on the inflation of claims (something like 8% to 10% a year for third-party, based solely on court judgements and out-of-court settlements, and 3% a year for own damage, based on what motor manufacturers and garages can get away with charging), motor rates ought to be going up by 6% or so a year. Instead, for much of the last decade, they've been static.
As for your comment about variability in premiums - if an actuarial team had data from the entire motor market in the USA to deal with, and only 5 or 6 rating factors, then they could get a very accurate rate. Instead, no-one's got more than about 10% of UK data, and they're working with over 20 rating factors. In those circumstances it's amazing that anyone is able to make money.