Mixing different front and rear tires My used bike came with different front and rear tires. It appears to have some kind of Kenda commuter tire in the front, and Continental Country Ride in the rear. They are both the same size (700x28).

Is this perfectly acceptable or should a bike always have matching models (and/or size)?

My main concerns from mismatching tires:


Grip thresholds may be inconsistent
Ride comfort? 
Wear rates (but rears seem to wear faster anyway)
It's perfectly okay to run different sizes, brands, and types of tires on the front and rear.  As you note, rears will wear faster due to carrying more of the load.  The grip threshold is largely irrelevant, since the front and rear will be exposed to different forces and grip requirements.

The main concern is keeping within the range of a single tube size if possible, since otherwise you'd need to have twice the spares on hand.

At the extreme end, there are 69er and 96er mountain bikes that mix and match 29" (622) and 26" (559) wheels on the same bike as well as Terry women's bikes with 24" (520) front wheels and 700c (622) rear.  By necessity those run very different tires front and rear.