The hatchback you have came with a zetec which is one of the most reliable engine platforms that I know in the car. I havent heard of any problems with the 02 zetec. I believe your mechanic is referring to the 2.0 spi engine which is know to drop valve seats thus destroying pistons and catastrophic failure.
2003 Ford Focus ZX3("FUBARCUS" was "Brokus") - old and still busted
2007 Subaru Impreza 2.5i - current DD