Example:
http://www.ca.com/ca/en/news/Press-Releases/na/2013/CA-Techn...
"... seeking ... an injunction against AppDynamics prohibiting the infringement of CA Technologies patents"
In case CA wins, the court will prohibit AppDynamics to sell any product that violate CA's patents.
Yes, one may host the company in Canada. How to sell to US customers though? VISA, MC and AMEX all have US presence and will comply with the court order (CA's lawyers will undoubtfully provide a copy). Paypal and other various Stripes are just facades to the very same VISA et all.
Without ability to charge for the product, where the business is going to be?
Getting an injunction against a company outside the USA for software running outside the USA is not within the claimed jurisdiction of US patent laws.
Now, step two: US trolls will not sue a company doing business outside of US; too much trouble. But any company doing business in US is a subject to local laws, and most SaaS companies want to work on US market simply because it is the biggest one.
"Doing business in US" means, among other things, having US customers and using US payment processors.
Only if you're a hardware startup.
If you're doing software as a service and you can deal with latency issues, you can operate many places where US patent law doesn't apply to you or to your customers. Canada and Mexico have high speed connections to the USA and Germany or Korea aren't so slow either.