This forum probably represents .01% of Toyota owners... and the people here are the fans. A thread proclaiming the virtues of any car in a forum of any kind is virtually meaningless statistically.
I've been in the auto biz for 30 plus years and seen millions of cars go through auctions and dealers. 300K simply does not represent ANY group of vehicles on a regular basis.
I am sure there are a few. I recently saw a Chevy Malibu with over 250K at auction that was still running. That was a really hard one to believe. Heaven only knows what they had to replace to get there.
I still find in nearly impossible to believe anybody could sit in the same seat and drive the same car for 300K miles. Sheer insanity.
Define many. I already stated it's a subjective discussion.
How many cars are built? Of those, as a percentage, how many will go to 300K? How many 2003-2008 Corolla, Matrix and Pontiac Vibe models were built? As a percentage, how many will go to 300K? Nobody here has answers to those questions.
If you even read the threads, they were even meant to display "virtues" of any kind. Rather one is for owners to post/report mileage and the other was to discuss the cluster maxing issue.
As for that fact that most cars, regardless of brand, model, or year, will not go 300K. That is likely true. However YOU asked HOW a Matrix (a 2003 no less which is the worst model for issues), went 323K as if it's an impossible task. You then related how in your experience you have seen many bad examples and without any explanation suggested no reasons WHY 300K is not achievable and suggested you were being sold something. When given a thread of examples of these cars going over 300K with actual documented examples and an explanation of the means to achieve that goal (good maintenance), your reply makes new baseless insinuations to support a counter point to an argument NOBODY MADE.
Why could someone go 300K in a vehicle? Maybe they are in sales or have a long work commute. Maybe it's 6 people who owned it at different times. Maybe someone just likes it that much. People have widely varying reasons for why they do anything. My Sequoia has 215K and has needed only minor maintenance and repairs (door handle, bulbs, etc.). Even with the widely report issues of Air Injection system issues, it has never had a reported fault in nearly 12 years and the above listed mileage. Vehicles sold through dealerships are also not representative of all vehicles on the road. There is less incentive to trade a 300K mile Matrix vs. selling it privately.
Your initial post added nothing of value to the discussion and was probably meant as a joke. I really don't see the point you were attempting to make by continuing forward. The OP is trying to get help on an issue relevant to their vehicle. If your only intent was to reply in an attempt to poke fun over owners and enthusiasts on this particular forum, shame on you. That won't be tolerated and you should know that better than most. If not, well I think we can agree that OP get an answer to their questions.
OP like others stated, your issue is likely wheel balance caused by imbalance, a bent wheel, or defective tire. Have it looked at by a tire shop.