The IP address you're using inside your house should be an IP address that isn't routable over the Internet. This is a really good thing, as it makes the Internet more scalable and predictable. So the packets you're sending have to be changed at your firewall from your house's external address to one that would work internally. While most routers are easy to configure to do this for standard TCP connections, special packets like the WOL packets are different. They're also likely to be dropped by ISPs as a "bad thing", much as a postman might refuse to deliver a seethrough plastic bag full of rotted meat. There might be a use for what's inside, but more than likely the person on the other end doesn't want it.

I've used the Linux box running on a PC inside my firewall to originate WOL packets for other things inside the house--but that was after I got "inside" the house by logging on the PC via ssh. If you want to make this more easily accessible and you already have a web server running on the inside, you could set up a web page that runs a WOL command when the page is accessed. You're not opening a new security risk, just a "waste electricity risk".