At the international level, I normally see games that are either decided by a draw or one player resigning. It seems that players at the international level don't let the game result in an actual checkmate, and resign before that happens. Do actual checkmates still happen at the international level, or has it pretty much stopped?
In my own experience, which is not international, I used to play games to the very end; even if I knew I was going to lose, I always lost by checkmate. Later, I came to the realization that it was pointless to drag games on that I knew there was no chance for me to win, so I mostly resign now. This sometimes has a negative impact, especially against weaker players, because sometimes when you are losing there is still a chance to salvage a draw.
Generally speaking, it's true, high level games don't play out all the way to checkmate. But there are some exceptions, and the most typical scenario that I have seen for this is a game that features, say, a nice, well-conducted attack, perhaps with a pretty mating pattern or particularly nice combination, and the losing player allows mate to show up on the board as a gesture, a congratulatory "hat tip" to a quality piece of work. For example, I believe that was the case in the game Adams - Short (London Chess Classic 2011).
Other than that, there are also the occasional instances where mate occurs during a time scramble. Or even more rarely, a top player might just overlook a mate in one and end up getting checkmated: it can happen to the best of us. Edited to add: Just the other day at the Olympiad in Istanbul, GM Dragan Solak of Turkey had a similar slip-up against Nakamura, overlooking the fact that a pin on his f7 pawn made possible a sort of epaulette mate: