Nope, we're talking about street.Street portraiture
There is a significant difference between "street portraiture" and "street photography". Now really there are no rules and no strict definitions; you can shoot what you want and call it what you want but most of what is posted on the forums from new street shooters is better classified as portraiture. If you're focusing on just the faces of random people on the street, then yes, I'd say you want a longer lens.
But in the vein of classic street photography you really should show context -- where do those people live? what are they doing? why are they interesting? what are they doing that deserves a photo? If you can't answer those questions about the person, why take the image? What do you hope to show other than a random person's face when they didn't know you were taking the picture?
Viewer involvement in the photo is an entirely different story. Using a long lens creates a distant, anonymous feel to the photo. The background is usually blurred out removing all context. Space seems compressed and the person looking at the image will not feel involved.
Contrast that to something taken with a 28mm or 35mm lens -- much more of the scene will be in focus and the perspective given is much closer to how we normally view the world. We have a very wide angle of view with our peripheral vision.
Street photography (candid):
(posed or pre-arranged with the subject, but still with wide angle):
As I'm fond of quoting Robert Capa, great Magnum war and street photographer -- "If your pictures aren't good enough, you're not close enough"
Please see the images of Bruce Gilden... look how close he is! I love them...http://www.magnumphotos.com …R1482X4&nm=Bruce%20Gilden