The only problem is that Rick's coma and all dialog referring to it are straight from the comic. The comic has made no indication that Rick is special.
From a story stand point it cheapens the peril and grimness of the situation if Rick has some special immunity.
I think people are reading too much into Shane's "I thought you were dead" comment (which is the only "hint" that has been made, contrary to self reinforcing rumors on the internet). We already know Shane wasn't the sharpest knife in the block and definitely not a doctor.
As for Herschel, that scene was the definition of "cheap thrill" and playing to audience expectation for the scene.
Right, and also Shane was in love with Rick's wife. What better opportunity to get Lori to fall in love with him? I don't even think that was conscious on Shane's part because he never believed that he was a bad guy.