The discrepancy in the numbers can partly be attributed to refusals, but I think a number of employers look at a number of options to meet their HR needs, and temporary foreign workers would be part of that strategy. In effect, sometimes an improved labour market opinion may not actually manifest itself in an application with CIC for a worker, but of course there are refusals, as you have mentioned.
When it comes to the way the program works, HRSDC does deal with the employer. Their role is to establish whether or not there is a legitimate job from a legitimate employer with a need that cannot be met domestically.
When it comes to the actual issuance of the work permit, it is CIC's responsibility to determine whether or not the applicant that the employer has identified has the ability to do the job that's been offered; that they have the acceptable experience, as outlined in the labour market opinion; and if, finally, they are someone who, in the opinion of the visa officer, is going to return to their home country or leave Canada once their work permit has expired. Those are, grosso modo, the assessment factors that our officers take into account.
You mentioned low-skilled. I think there are some instances where perhaps people may not have established to the satisfaction of a visa officer that in fact their ties to their home country would be sufficient to have them return to their home country after their work period.