(edit)The question is about web companies, located outside US but selling to us customers(software,web apps, ebooks ... - digital products).
In Germany for example there are insurances, that will cover your costs of lawsuits etc. when you accidentally infringe IP / patents. They will also cover if a client sues you for lost business because your product somehow failed in a bad way. Some of them will offer worldwide coverage, but every policy will exclude US lawsuits.
I once worked for a very small UK company which ran into a patent tussle with a rather larger US competitor, as the former didn't want to exclude such a large market for potential sales. Evidence of prior art was collected, with the outcome being the overturning of their patent - at which point, a nominally amicable resolution was found.
Software patents certainly pose challenges - even if the idea seems straightforward, if it's something fundamental to the design, you'll need to check for possible US patent conflicts if you want to enter the US market, or may in the future.