Wait, doens't Nintendo refresh the patents?

There are a lot of patents or copyrights that are no longer refreshed by the companies who hold them. I do not know about Nintendo consoles though.

Thing is, even if patents are still pending, clones are not necessary illegal. A company can allow other to use their patents. The thing with clones is that Nintendo doesn't care about them.

They stopped making NES and NES games long ago. They no longer get revenue from the console. Also, most people don't care about 25 year old consoles. Companies making clones do not make a lot of money off them (compared to current-gen consoles) and they do not hurt current-gen consoles sales. It would be more of a pain for Nintendo to sue people who make clones or ROMS or whatever of old consoles rather than let them do their thing.

So go ahead, download any ROM or any ISO off the internet and play them on emulators or clones, no one will care enough to stop you. If anything it could allow Nintendo to make extra sales if for example you were to play the old Zeldas unlegitimately, then like the series and buy Skyward Sword, A Link Between Worlds or Wind Waker HD (plus the consoles those are played on of course).

The only thing I see that could piss them off is that they make less sales of Virtual Console games, but those don't bring in the revenues the new games do, so they don't seem to mind that. They just know there is a market for retro games and people stupid enough to actually buy them because "Hey! I can play the original LoZ on my Wii now! Thanks Nintendo!".

I think Nintendo sued a clone company once but they lost the cause, plus it was before 2003, the year the Famicom patents expired.

As for retro gaming a lot of younger people will just download games on emulators (or a flash cart) or buy them digitally for cheap rather than buying expensive cartridges that you have to blow into or clean, because they don't care as much about the nostalgia factor and it's cheaper (I mean, Earthbound on the VC is $8 maybe and in cart form it's $160.

I have a NES/SNES clone called RetroDuo, but I heard that sometimes it had overheating problems and could produce smoke when used for too long if defective, plus in my case it is even harder to get NES games to play in it than my actual NES (which is quite ironic considering I have the front loading model). Same for SNES. Retron is apparently quite good, though.

Yeah such as Mario RPG. More recent clones such as the Retron are pretty much emulators, though, so the compatibility is pretty much identical to ZSNES and Snes9x. As for having the real thing, remember that you can plug real SNES controllers to some clones. The ones that come with it usually suck (although the 1997 SNES gamepads weren't that much better).