I understand this law, but I've always been frustrated by it, as I've always been told by both Apple Retail and Apple Online that they are two SEPARATE entities (which is why you can't always exchange online purchases at a retail store nor can you have orders shipped from Apple online to a retail store and pick it up).
So what are they, the same or different? If the same, why can't I do the same things with each store? If different, why am I subject to sales tax?
If what you were told is true, I would suspect that they are separate sub-entities, both owned by the same parent company, which would explain why they collect tax.
Either way, there is a huge difference between Apple charging tax (which they don't do, your state charges tax) and being required to collect tax. Besides non-taxable goods, you are legally supposed to submit tax for your purchase. The only difference is who submits the tax. If a company is required to collect the tax (not charge), then they submit it on your behalf. If a company is not required to collect tax (again, not charge), then you are legally supposed to submit the tax to your state.