Ok, I should have been more specific. Let's say I get an email with a sweepstakes, and it says for an additional entry to like the sponsor's FB or Instagram page, wouldn't it make sense for my Android pbone to offer me the option of opening the link in the corresponding app? Do you think that's something that Android OS should do, or is it a flaw in the e-mail? Or do you still think it is perfectly normal?
Why do links in Web pages open in Web pages even if you have the app installed? For example, I tap a link to like a Facebook page, but it opens in tge Web browser, and I'm not even given the option to open it in the Facebook app.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic