Expectations from software are lower than other products like cars, televisions. A car breaking down in the middle of a drive to work is far more "severe" an incident than Internet Explorer hanging and crashing. Further, software engineering as a field is very very young, with a far lower barrier to entry, resulting in products and processes which are much less evolved and mature compared to other industries. I think these are important factors why software tends to have lower quality bars than cars or physical products.
