Yes, but the question at issue is, "what's plausible in the natural world & what's not?" In an experiment you'd purposefully change the temperature up or down, but that's perfectly valid as long as temperatures go up & down in nature.
As for the bacteria, the question was, "where does the ability to survive in the face of antibiotics come from?" You can't answer this as definitively in the wild as you could in an isolated lab environment, since you could never be sure it was the test bacteria that evolved, nor could you be sure that some kind of lateral DNA transfer hadn't occurred from another species of bacteria, etc. That's why the lab experiment is so powerful.