Eh, all in Costa Rica and seemingly none of them have support for English-speaking customers. This isn't a representative sample of the worldwide Internet. And by a margin so wide that it makes your statement laughable.

From my experience trying to support the use of Bittorrent (both commercially and individually) and various RPC stacks (commercial support for home workers) I can say that the "complaints" don't equal the real ISP problems. Only somewhere between 1% and 5% are the real provider-caused blocking/interference/mishandling. The remaining 95% to 99% is on the customer-caused misconfiguration or hardware/software faults.

Many ISPs, used advanced filtering products to protect their network and clients like http://www.cisco.com/c/en/us/products/security/security-monitoring-analysis-response-system/index.html , so even if they aren't overtly blocking TCP on port 8333 but their firewalls and filters are because it is detecting a suspicious transfer.

You can test for 8333 being opened here - http://www.yougetsignal.com/tools/open-ports/ and if you don't have more than 8 connection in bitcoin QT you are not accepting any incoming connections on port 8333.

Sometimes its a local firewall blocking you or you need to either allow UPnP or port forward to get QT functioning as a full node but in many other cases its the ISP themselves.

Regardless of the exact specifics with each case, most users aren't acting as a full node and the numbers back my claim. The average user isn't going to call their ISP , or create a forwarding rule in their router and make sure their firewall is configured properly.