The BBC News website use of Twitter comments is starting to really grate on me, and I feel it devalues the rest of their content. IMHO the only time they should be using them is when one of the parties directly linked to the story posts one (like the footballer hit by a coin today). Anybody else's thoughts is just irritating, like the complete random who'd tweeted "Level crossings are death traps" and ended up with is posted on the BBC News article about the level crossing incident near Doncaster during the week.
Surely if they wanted Piers Morgan's opinion, they could have just rung his agent and asked for it, although I get the feeling halfway through dialing the number, the journalist probably would have gone "hang on, what am I doing? Nobody want's to know what morgan thinks" and put the phone down.
Because it's quick, cheap and easy. Why make things more complicated than they have to be? Twitter offers a direct link to a person's opinion and, in my opinion, using it to illustrate a news story is no different to quoting a publicly released statement. If I'm right, Chris Lintott's tribute was lifted from Twitter, as was Brian Cox's.
With regard to your point about complete randoms, fair enough, but again, how are they any different to voxpop talking heads on the street? In these DQF Daily-Mail-fearing times for the BBC, maybe lifting quotes from Twitter is an easy way to fend off criticism about their use of our licence fee monies.
Off topic, but by the way, level crossings are only death traps if you're an idiot.