I think that there is a slight human tendency for some people to become more obnoxious the more seriously they take there pastime/hobby... Quite a lot of cyclists take it very seriously.
This is unfortunately a very true observation!
Of course it doesn't have to be lycra-clad-shaven-legged-carbon-straddling roadies who are guilty (I absolutely agree with those who warn against judging by appearances), but these are typically the people who have sunk the most time and money into their hobby, and are most likely to have their self-worth linked in some way to their cycling ability. IMHO those who feel the need to re-assure themselves of their superiority by making these sorts of comments have some serious ego related issues and deserve contempt (and perhaps a little pity too) as well as disapproval. Either that or you're in "their" way and deserve the abuse for interfering in their "serious" training - equally bad if they mouth off at you as a result. Of course, you also get some people who are plain d*ckheads and think it's funny and clever to upset people, and they could be riding anything (or in the car, on the footpath etc)...
Fortunately there are plenty of "serious" cyclists out there who are full of nothing but mutual enthusiasm and encouragement for anyone out their on the road, and just like to see people out enjoying themselves on the bike - these make up the vast majority of lycra-clad roadies I see out and about, and this forum seems to be full of them too.
It must be absolutely awful being the target of this sort of abuse - the only thing I would say to anyone who suffers from it is that the idiot spouting it is probably the biggest loser out there on the road today, whatever speed they sprint away, while the victim is an absolute winner if they carry on riding and keep on getting out there on the bike in spite of it.
My wife gets the odd comment when she's out and about, but nothing like the story that the OP linked to!