I am sorry, but these are very poor excuses! If even someone as technology and security aware as you reuses his password on various sites, what are the chances that there will be a few people who are not as aware (but still very interested in entrepreneurship), and they use the same password for banking, email etc? And what's the cost of providing SSL support anyway? Almost nil.
I know people sometimes try too hard to justify PG's actions. But, PG is a big believer in making products and services extremely simple for the users. It is surprising that he would expect users to be careful enough to not use their primary passwords on HN. The only excuse that I can believe is that he simply doesn't have time for it.