It is important to understand this "learning on the job" thing. It's no use hiding the basic fact: just as with the salary, there is a conflict here between your interest and your employer's. When you are learning, you are not producing and what grows is your market value - the employer might have to pay you more to keep you at the company, so for them the benefits of having a trained employee are at least partially offset by this fact. To put it bluntly - if at all possible, grabbing an employee whose learning cost is already covered by another company looks much better from the profit perspective.

It's not to say that learning on the job never happens - just as with high salaries, there are obvious situations when the employer can afford to pay you more or take the cost of your learning. The less they compete on cost, the better for you.