I've often wondered the same thing. I know we've had people post on here saying their piston/ring "repairs" failed shortly afterwards, but it's hard to judge what the cause of that is/was. Could be that the engine was too far gone. Could be the experience level of the people doing the work.
My guess is that Chevy initially had the dealers rebuild the engines with the same parts, until they found it was a virtually fleet wide problem. After which point the failed parts were superseded by redesigned parts (WE HOPE). This probably all took some time, so likely many cars went back together with the same parts that failed in the first place.
My wife drives around 30,000 mi/yr and bought this car new in early 2011. I believe 2010 was the first model year for the 2.4. When the timing chain was rattling, the dealer didn't believe it, and when the chain actually broke, they were shocked and demanded to see things like oil change receipts etc... this was before it was well known that these engines had timing set problems, as the rest of the fleet was way below us in mileage.
The (factory new) replacement engine took 2 weeks to get and it contained the same flawed parts as the vehicle originally had. The replacement engine had 3 years, 2 months and 80,000 miles on it when I took it to the dealer for excessive oil consumption. Of course by this time the flaws were well known and the dealer was not surprised to see it drinking oil.
I missed the warranty period by 2 months (3yrs, 100,000 miles on dealer replaced engines) and so I ended up having to negotiate a deal to have it rebuilt, in the end I paid around $1000 for the TSB to be done that replaces the pistons/rings/and timing set. That engine was slap worn out after 80,000 miles... the timing chain was rattling again, it was burning oil and they found a cracked piston wrist pin bearing (or upper connecting rod bearing... don't know what you call it)