Yes, but I still have to wait for the game to spawn what I want before I get a chance to catch it. The systems are more alike than you think, one just happens to cut out excess time many of us don't care to waste. I don't find excitement in constantly rolling wild encounters, I roll my eyes and go "ugh, another common."
I guess it could be done similarly if you make the spawn rates have these chances, but I imagine when you're looking for those, you'd have to run around to see if the one you're looking for is there, leave, and come back, which sounds much less fun than stepping back and forth in a patch of grass and running from encounters you don't want.
Also I missed this earlier, but Pokemon stay on screen for a limited amount of time. You don't have to leave an area to spawn a new crop, they're constantly spawning and despawning.