If I can create an adhoc wired 'network' so easily, then why is a wireless solution so much different. The comm's should be the same, so we're only talking about the means of transmission (is landline v mobile telephony is an appropriate analogy?)
Ad hoc was originally intended to be a means of doing rudimentary file sharing between PCs. A way to avoid sneaker-netting. Sort of like the basic capabilities in the far more sophisticted AppleTalk sharing services running on Macs. It wasn't intended to replace a traditional LAN. And it especially was never intended to be used as a router. That was supposed to be handled by internet connection sharing where one PC in your home network shared its internet connection with all the other PCs. So once again, one PC becomes the gateway of last resort as SJ put it.
Also ad hoc networking is a topology. Ad hoc networking can be done in a number of ways. It's not dependent on specific hardware per se. And it doesn't need a wireless capability to make it work. You could do an ad hoc network with a crossover cable and two NICs. Or with multiple PCs, cables, and a dumb network hub or switch - no router required. That's how it used to be done before wifi came out. Using a wifi connection just makes it much more convenient.







Or cables and a network hub (or switch) to plug things into. 






