[lmns]

That's true for TCP as well. Almost all consumer-grade routers block all incoming connection attempts, not just UDP.

From a stateful firewall's point of view both UDP and TCP have state.

[trav4225]

Right. I was assuming that the context here was connections being initiated by the client (as most are).

[kelnos]

... in which case blocking is not an issue. Consumer-grade NAT hardware will no more block client-initiated UDP than it'll block client-initiated TCP, at least not without extra configuration.