Dead on with the first 3. I also think Prudie picks the most emotionally flawed letters - because that will push her closer to the Dr.Phil ideal of "entertainment through schadenfreude! You're not as bad as this tool!"

But with the fourth.. I don't think it's necessarily about "lucky to have someone around" - that'd be appropriate for a date/best man/etc. The first sentence says that the circle of friends is "close-knit but ever-widening." Those two are opposites. If close people ask, tell 'em.. if people who aren't close ask.. they get the tactful but firm response. The problem, IMHO, is the inability to recognize the difference between a truly close friend and a recent acquaintance. It's not snippy/aggressive to not tell everything to someone you just met! It's actually normal and correct to slowly integrate other humans into your life, and make decisions carefully about revealing details.. even for folk who are just friends. It's called boundaries, and the Facebook generation will have trouble establishing those.