Depending on your definition of "top of the line", I don't think Nintendo has had any sort of monopoly. I would argue that in most terms, the PC has offered a superior gaming experience for most points in the history of gaming. Where it falls down is the supporting needs of gaming, such as system maintenance, game installation, etc. Even so, I think the top of the line title could be said to have been on the PC.

But hey, if you want to compare Doom on the PC when it came out in 1993 to Doom on the SNES when it came out three years later, and consider the sub-standard SNES port that's three years late to be a top of the line game, go ahead.

Although why Doom was used as an example (not by you, I'm aware), I'm not sure. I don't remember any copy protection on it.