Uh, there is strain relief. On every cable. You're probably doing what everyone does, which is to wind that cable on the power supply as tightly as you can around the charger, which is going to eventually break the cable. Instead, make a small loop where the cable begins, then wrap gently. It will last essentially forever.

And no. This isn't a "well known design defect". In fact, Apple's cables are inevitably designed and manufactured better than competitors'. Have you even seen the awful mess that passes for PC power supplies lately? At all? Well, I have, since I administer about 200 Macs and around 75 PCs. I can tell you that there is no comparison in design or quality.

I have a MBP from 2008 with the original t-shaped magsafe power cord, and its still in perfect working order. Maybe you're harder on you're harder on your power cables than you're giving yourself credit for.