Not true. American jurisdiction is valid on the American soil only. Take an example of Microsoft who has bunch of generic software patents - software patents are not valid in Europe, therefore Jolla cannot be sued for infringement here. When you see patent wars, the result is usually either an agreement (like when Android manufacturers are paying ~$15 for each device to Microsoft) or a ban on sales in that particular country (like some Samsung devices in the US) followed by a fine.

We are not talking any crazy speculation; Jolla's management has stated in interviews several times that it is, in fact, the reason for not selling the phone in the US.

It is not the sole reason, though - the second reason (and also an important one) is the state of the US phone market. Unlike any other market I know, it is completely controlled by service providers - people don't buy phones in a (e)shop, but from Verizon/ATT/etc. . Therefore it is almost impossible to reach any significant sales for a startup.