"To the extent" being operative. It'd be good to have numbers substantiating this, because all signals indicate that US truck manufacturers have very little presence in European markets.

> US truck manufacturers have very little presence in European markets.

If they have any presence at all then they are subject to European regulations of one form or another.

For the units they deliver to those markets. You haven't demonstrated that the US models are being adapted to European requirements, rather than companies selling European adapted models. My understanding as a lay-person is that the latter is much more common, since the European market requires adaptation anyways (more diesel engines, more manual transmissions, different driver side, &c.)