Well, you wouldn't, unless the title company messes this up. And there are lots of other ways the title company can mess up any transaction, so you have to trust them to a degree anyway.
The confusion comes up because the IRS doesn't collect FIRPTA from the seller or the title company but from the buyer. If everything goes as it should, the title company withholds the 15% and sends it to the IRS (or holds it in escrow until they receive a withholding certificate).
Although you haven't written this, the general tone of the discussion here makes it seem as if the buyer is liable for a tax that the seller has neglected to pay. But this isn't the case. It's the buyer's responsibility to withhold 15% from an international seller in the first place and the title company typically does it for him.
What you and others are suggesting is to reduce the offer price because you don't want to be exposed to the risk of having to deal with the IRS (which is only a problem if the title company doesn't handle this correctly). This is, of course, your prerogative, but in many cases you will probably be outbid by someone who trusts the process.