Bearings and water pump - premature replacement?

[MrDisco]

I have an 09 LE V6 purchased new from the dealer and maintained as per the maintenance schedule. It currently has 74,000km (approx 46,000 miles). The car is used mainly in the city with typical stop/go traffic.

Lately I was experiencing a low rumble while coasting. The dealer took a look and replaced the front driver wheel bearings. The noise is gone but my questions are:
-is it too early for the bearings to go?
-what causes the bearings to get damaged?
-do both sets of bearings need to be replaced (front and left)?

During the same visit they discovered the water pump was leaking so they replaced that as well (thank goodness for ECP). similar questions as above:
-how long do water pumps normally last?
-what causes them to leak?

Thanks for your insights (sorry for the n00bish questions). I'm a little disconcerted that parts are starting to fail so early in the car's life cycle.

[JohnGD]

Seems common for Gen5+. I wonder if it's a problem with the pink coolant (Toyota super long life coolant). According to Aisin they're using carbon ceramic seals in the pumps, and the unitized seal isn't anything new if the manufacturer can handle a decent level of precision.

Aisin pump and carbon ceramic seal:
http://www.rockauto.com/catalog/moreinfo.php?pk=1872126

I'm more inclined to flush the system out with distilled water and switch over to Valvoline G-05 (with 50% distilled water) from the local NAPA store. I'd try another Aisin aftermarket pump with G-05, or just switch over to a Bosch pump that can handle low-silicated coolants like the G-05.

As far as wheel bearings go they should easily last 120-150K miles (~193-241K km). So 46K miles is too early. Maybe a lower cost part? Bearing seal/moisture/lubricant problems? Alignment? Ask the dealer to keep the old part next time and see who makes it. Koyo or NSK should be decent.