I was referring to this (emphasis mine):
"How many times have you gotten/sent an email when wondering what kind of character you could make, and a reply comes up with something like, "We have a Rogue, a Druid and a Sorcerer." The implication of course is, "Make a fighter-type", but in fact, the email is useless.... Instead the email should say, "In combat we've got a Tank, a Striker and a Battlefield Controller, another Tank would be great...." Characters are too flexible in D&D to define role by class. Instead the role should be defined by what they do."
It assumes that each player will build a character to do one specific thing, and that thing will line up with one of the 4E categories.
I think you're looking at the statement too narrowly. When I do a party-optimization exercise, I do list all the roles I can think of and make note of which party members fulfill those roles and how many roles they fill. E.g.
Paladin of Devotion/Wild Sorcerer/Cthulock: Tank, summoner, counterspeller, ranged specialist, secondary healer, secondary artillery, tertiary scout, communicator/diplomat
Shadow Monk: Scout/intel specialist, disabler, secondary tank, secondary ranged specialist, communicator/diplomat
Bard/Cthulock: Healer, summoner, ranged specialist, counterspeller, secondary scout, communicator/diplomat
Necromancer/Cthulock: Summoner, ranged specialist, counterspeller, artillery, tertiary scout, communicator/diplomat
You can classify the functions/roles however you want, but the point is that you should think in terms of capabilities and not just classes. All wizards are not created identical and equal at all tasks. Even something as simple as whether you have Stealth from your Background, or whether you learned Invisibility, can make a big difference to your capabilities.
I'm inclined to cut some slack to treantmonk. It's a one-sentence example--he can be forgiven for not saying "We've got a [Tank, summoner, counterspeller, ranged specialist, secondary healer, secondary artillery, tertiary scout, communicator/diplomat], a [Scout/intel specialist, disabler, secondary tank, secondary ranged specialist, communicator/diplomat], and a [Healer, summoner, ranged specialist, counterspeller, secondary scout, communicator/diplomat], so it would be great if you would bring someone who can broaden our utility spell coverage and maybe supply some powerful front-liner summons when necessary while retaining some stealth capability for infiltration scenarios." That example, while realistic, is so complicated to parse that it would obscure the point he's trying to make.