I doubt they are. Back in the day (and hopefully still now) they were pretty mature in market research.
WOTC_Trevor commented on this several times on the L&L thread over at community GA. Pretty much said the same thing. There are going to be 2 choices, no, this isn't really market research, but they feel it is pretty much worthless to have middle options.
Of course my feeling is much like others here. There's really no point to it. I can tell you with what I'm sure will be 100% accuracy which options will get more votes and which polls are going to be tilted to which extreme. I seriously doubt anyone over at WotC (or really almost anyone that would read L&L) couldn't do the same.
[MENTION=82617]Camelot[/MENTION] (et al) I disagree. I think all 4e characters are heavily weighted into the 'team player' mold. SOME characters can function in a limited way on their own, but not very well.
Controllers simply have no point on their own. The wizard is in the best shape here as he can fall back on a fairly deep set of utilities and rituals, and can at least do some credible range attacking if need be. None of the other controllers as I see it are as capable, though the Druid at least has some pretty robust class features and summons help. The Invoker OTOH is pretty well useless.
Leaders are frankly pretty much porked. A STR cleric can fall back on bashing things, but he's going to have a rough time. Warlords are neigh useless on their own. Bards are nearly in the same boat in combat as the warlord, though at least in other situations they have a deep skill list to fall back on in general.
Strikers are a very mixed lot. The barbarian is fairly tough and has some awesome nova potential, so he can maybe bull through. The rogue can sneak around and play sniper. The others are all kinda iffy though. Warlocks are pretty much dead meat, though there are so many possible builds there it is hard to generalize. The melee ranger is probably worst off of anyone. The bow ranger can at least hope to cause significant pain before he's cornered. Beast Masters are probably best off.
Defenders in general probably are overall the best off, especially the fighter, who can do a credible striker imitation and is generally quite tough. Paladins can do OK, but have limited options. The warden is sort of the reflection of the barbarian, limited damage potential but they can at least slog through head-to-head, and at high levels tend to be pretty self-sufficient.
OTOH outside of pure combat situations, which presumably won't come up as much when you're alone, all classes have some depth and certainly can pick up options that are useful in solo situations. The fighter is a bit shortchanged there, but even so the skills he does have are likely to be pretty handy in a lot of cases.
Anyway. I think if you account for the types of situations that solo PCs are likely to be placed in they do have pretty limited combat options. OTOH they can generally operate in other situations, though not all of them in any given scenario. I'd be hard pressed to see any major advance made in this area on what 4e offers. It is kind of a zero-sum game. Less team oriented design would simply be less teamwork, and more would be overkill.