The number depicts the ratings and package of the transistor.
An off mains switch mode supply needs a transistor of at least 700v rating.
A car 19v laptop switching converter only needs one of around 50v.
You might find the switching trans in each to look the same, but as I said will have different ratings, therefore will have a different type number.
What makes you think that, since a transistor is used as a switch, the various transistor parameters that affect it's use as a switch and differ between transistors aren't important?
Ib saturation curents, Ice MAX. Temperature vs current, cut off current - many things. It depends on the input signal, and load you are switching. Imagine if you have a really low current signal, and wish to sample it to use as a switch. You would want to use a high gain transistor and low cut off current to sample the line to achieve saturation.
I rather expected you to came back with that question. I realize your favorite hobby is thinking up more questions to ask on a myriad of subjects, but as a little homework exercise I suggest you look at a transistor data sheet and see if you can determine which parameters might be important in using a transistor as a switch (such as this 2222A). That's how I learned after I started doing design work after leaving school, it was not taught to me. I believe, for the most part, the answer to your question is fairly obvious. Information obtained that way is much more useful then if it's just handed to you. Much of engineering involves logical thought and this is a good exercise in honing that process.
Ib saturation curents, Ice MAX. Temperature vs current, cut off current - many things. It depends on the input signal, and load you are switching. Imagine if you have a really low current signal, and wish to sample it to use as a switch. You would want to use a high gain transistor and low cut off current to sample the line to achieve saturation.