Lab tests aren’t always conclusive of how a device will work in the real world.

Take the iPhone 4, Apple has plenty of test labs yet they could not predict the antenna contact issue that resulted in “Antenna Gate”.

Also mind they are trying to get these products out before the competition and that doesn’t always give time for field trial testing.

While a design defect could delay release for months and once released it’s usually too late to expect any significant design changes.  Especially in a market that will be pushing a new model in a couple months to a year anyway.

The real world testing is mostly irrelevant given the short period they usually allow and the high level of security prevents full free reign usually needed to fully test devices in all possible usage scenarios, along with usually too small a user base sampling.

After all, that didn’t prevent the iPhone 4 from being released with its antenna issue.

While for the original Transformer, there was no notable design flaw.  Just the software took time to work out but that was mostly Google’s fault and not Asus.

For the Prime, it is Asus fault for the GPS and WiFi issue.  Though it may not be so much a design flaw as a manufacturing defect as at least one reviewer noted that pressing on the area that the antenna wire connects seems to fix the issue and means it may just be a loose connection and why it may have gotten past their product quality control…

http://www.youtube.com/watch?v=vgx2Kpfi-Ps

GPS signals are easy to block though.  So an external antenna is usually preferable for the best signal.