Isn't Steampunk about style and culture as well as technology?
I think one could imagine a world in which the culture of the Victorian/Edwardian era (continued social stratification, imperialism, global dominance of the British Empire and a handful of other world powers) survived well into the 20th century that is not ASB. One can also imagine a world in which coal and oil burning steam engines survived as the major source of power for utilities, many vehicles, and utilities.
But having this technology coexist with airships, airplanes, space travel, computers, or nuclear power is unlikely, since the technological innovations necessary for these things requires small and light engines, a high degree of miniaturization, and other advancements incompatible with continued reliance on steam power.
I have no problem with a "steampunk-lite" world that looks and acts Victorian with huge iron contraptions and belching smokestacks everywhere, and for that matter has cool things like steam cars and airships, but giant steam powered armored airships, massive land battleships, mechanical computers, and Jules Vernesque space travel is ASB, since you have to invent some impossible things to make these things possible.