Well from experience in the Netherlands i can tell most (large) corporate networks do block most outgoing connections. Often only outgoing HTTP / HTTPS is allowed (mostly via some proxy construct). But then again you are right that in these cases you are probably not allowed to install a non-standard device in the network (but often nobody notices as long as you use port 433 and preferably HTTPS 
).
But I guess these companies are not the typical use cases TTN is about: they are used to paying big money to Telco's for services with SLA's.