I still own my '03 Toyota Matrix XR 5 speed. Bought it new back in April '03. I logged 40mpg (US gal) on a recent trip from my home in Okla City to Guadalupe Mountains Nat'l Park in west TX. I accelerated gently and drove a steady 65mph on the interstate (and yeah I got my doors sucked off by drivers in Tahoes doing 85 mph).
The only things I've done to mine is new tires at 40,000 miles and a new battery at 50,000 miles. Still on original brake pads, with 40% life left. 60,000 miles on the odometer now.
I do have a Check Engine Light on, and when my mechanic read the code, said it was due to 'low catalyst efficiency'. A new catalytic convertor is required. Luckily, this repair is covered by the federally mandated 80,000 mile pollution control regulations. Other than this, it has been a very reliable and efficient vehicle.
And we see the same differences here... a Pontiac Vibe with same mileage and options as a Toyota Matrix is worth less at trade in time.
All the more reason to look for a nice used Vibe instead of a Matrix.