I think one of the tubes was a Performance "Lunar Lite". I'm never going to buy them again. Too much trade off with the weight.
I believe the other was a Continental.

Both of these tubes had more than a season on them. I patch my tubes, so sometimes my spare tube is a used patched tube. I do think that pressure cycling is a contributing factor to the failure around the stem. I probably do about 100 miles a week during the season and ride 25 mile weekends in the off season. I guess I average around 4-5 flats during the year. I'm really keen on this stem reinforcing idea. I think its going to go a long way in preventing stem failures. We'll see how it pans out.