This is a good point.
On the other hand, the current default, UDP, typically returns false even when pinging the local host (127.0.0.1). This, by itself, has caused so much confusion that there are posts all over the 'net asking, basically, "Why doesn't Net::Ping work?" My general idea for fixing this problem is to always use the most accurate ping available on a given system. If people can't be bothered to read the POD, I guess I consider that their own problem. On the other hand, I think the major problem here is that the current POD gives no explanation of why some types of ping are incredibly inaccurate.
I suppose we could default to ICMP, which would actually make most (non-root) people read through the POD before playing with the module.