"Let me check what's going on at Slide... hmmm... it doesn't work. I'll check $OTHERCLUB."
Expecting a potential customer to go find another device to access your content/promotion defeats the purpose of building said promotion. Similar is true for making the content/promotion difficult to find via a search engine.
The costs involved in the production of more accessible content are negligible. In fact, it's faster and easier than creating flash content, and you could automate most of it into a form based UI (image of flyer, title, date, time, descriptive text).
I do see your point how club promotional sites might not get a lot a traffic but keeping a promotional site accessible to mobile devices and easily found through search really does makes sense. Advertisements that cannot be seen are far less effective than advertisements that can be seen.