It's also possible that the ride itself reduces stress and that has a beneficial effect on the immune system.
My main concern from cycling to work is being able to have a shower when I get there so I don't stink everyone else out. I used to ride to work when it was close enough and now I am close enough again it is something Ive been looking forward to do to improve my fitness after recovering from injury.
The biggest issue I've had with cycling to work is some drivers. They approach from behind and don't realize that sometimes I'm swerving to avoid holes or other obstacles they would just drive over. Then there are some real jerks. Once when riding to work a driver positioned the front wheel of his vehicle about a metre or so from the back wheel of my bike and maintained that position while I was trying to avoid obstacles. Probably not the worst story out there but it shows that some people will menace you for riding a bike for no other reason than they can.
So I think the unmentioned thing in this article is all the bike riders that have suffered some injury because of someone driving a car and how careful you have to be so you don't end up mangled by one.