For those of you who might not know, steampunk is genera of sci-fi that takes place in a vision of the future that someone from the year 1900 might have had. It's one of my favorites to read because it can seem to be a mix of sci-fi and fantasy. So, of course I'm going to try to write some.
In my opinion, a good sci-fi story is free to speculate about any technology we are not currently aware of, but must not contradict what we already know to be true.
Steampunk has different limitations. It must not contract the understanding of the year 1900 (or there abouts). The trade off is that it should not accurately portray the understanding of technology that has been developed in the mean time either.
Is this more restrictive or less? I'm not sure, but its different, and that makes it more interesting to me.