I'm fairly convinced--and I'm tempted to conduct some research on the matter--that the people who say they don't "see" the sibling dynamic between the two characters either don't have siblings of their own, or don't have close relationships with their siblings.

That said, I was a little more into Sam/Daniel when I first started watching the show, but began to step away the more what I was seeing on-screen didn't match what I was reading. The final straw for me was an author-who-shall-not-be-named who was writing a supposedly-gen fic in which ship kept creeping in at strange moments. There would be scenes I would stare at the screen and ask, "WTF would Daniel go to Sam to talk about this? Wouldn't he go to Jack, first?" And then Sam acts all sympathetic and understanding, at which point I begin shouting, "But Sam's as emotionally inept as *I* am! She would TOTALLY not know what to say here, whereas Jack would say something inappropriate that would nevertheless make him feel better anyway!"

So... yeah. The work of Thraesja and Amaranth Traces aside, I tend to find that most Daniel/Sam 'fic relies on bad characterization to make the pairing stick.