One of the reasons for smack packs, and starters is to make sure the yeast is viable. If it doesn't matter then why go through the trouble?
It's nice if it swells up but if the pack is rough shape for whatever reason (age, partially frozen on delivery, etc) you might not get much swelling and still have viable yeast. I don't even bother to let it swell. I smack it while I'm boiling the starter and dump it in once it's cooled.
I just stepped up a year-old pack of Thames Valley and it was very slow to start, to the point where I was getting concerned. But I just let it go and it was fine. The batch of ESB I pitched it into just finished up primary fermentation about two days ago.
I hear what you are saying but if the wyeast website says:"Expansion of the package is an indicator of healthy (viable and vital) yeast."
and the package doesn't swell, one can't just ignore it. (I realize that that's not what you said) Maybe they should put something on the packs saying if "it doesn't swell this might be the reason and to take these steps"
I was ready to take that dead looking smack pack back to the store, not because I thought it wouldn't work, but because I payed for a pack of healthy yeast and if the pack doesn't swell I am not getting what I payed for.
Same thing with starters I see it often recommended to "pitch at high krausen"
and then I read a bunch of "I never see action in my starters"
Just saying, it gets confusing sometimes.