It seemed to me, just skimming the answers, that most said your standards aren't too high, but to relax them so you won't get frustrated. On the other hand, I would be on the side that would argue they simply are too high. Here is why:
First, everything you mentioned didn't have to do with major events. It wasn't that your car broke down and no one would help. It wasn't that there was a medical emergency and no one would watch your kids while you joined a friend or family member at a hospital. It wasn't about anyone helping take care of anyone else in a time of need. They were all about parties, which are non-serious (also non-necessary) social occasions.
Second, you're saying that even if a child is invited to 30 parties in a year (which happens with all the different classes-school, church, karate, etc), that child's parent HAS to invite your child. Uh...unless YOU want to foot that bill, that's a ridiculous thing to be upset about. People have to work with what they can afford, and usually do this by inviting family and a few closer friends. I struggled with this myself for my daughter's 4th birthday party last month. There were about 30 close family friends with kids in a similar age that I wanted to invite, in addition to our family members who totaled 9, plus our family which is 4. If only one parent came for the friends, I'd still have had 73 people. There's NO way that would work at the only venue we could afford (our house), and I simply could not have gotten all the groceries for it. Which would have been worse? To not invite, or to call everyone we couldn't invite and tell them I didn't mean to be rude, but they didn't make the short list. My true friends know I love them and understood without me having to explain.
Third, I was thinking the main reason to verify plans is that people know other things come up. For example, EVERY year, we celebrate Mother's Day as a family. EVERY YEAR. But when one of my brothers gave my parents Cirque du Soleil tickets for Mother's Day, it was understood that we wouldn't be celebrating as usual. Things happen, and sometimes when we prioritize, we see a friend we haven't seen in a year, or choose the family get-together, or we're so stressed b/c life has been unexpectedly crazy that we need a break simply for our mental and emotional health.
Fourth, not every email or call is easy to return. I am currently bedridden because I may be having a miscarriage, but if not, doing too much could cause it. Is that any of your business? Nope. But I'm telling you b/c life happens. I had someone else tell my brothers what was going on-they didn't even know I was pregnant, but I just couldn't deal with telling 3 more times what was going on. Sometimes I don't email right away because there's so much involved and I want to really give the person my time and attention (yes, even in an email). Sometimes emails don't ask questions or don't ask in a way that people believe a response is necessary (like rhetorical questions, or thought-provoking questions). Then maybe they respond to one where it is necessary.
I went over these step by step, so you can see where I'm coming from when I say it sounds like you're being petty and maybe a little selfish. You want others to consider YOU, but you don't want to consider THEM. Your standards are too high because it all revolves around these social events that are for YOU. I know, your dd being invited isn't about you, but you have definitely made it not about the other child or parent. You doing these things as a courtesy is very nice. If these were standards you set-to reciprocate invitations, to RSVP, to never have ANY conflicting plans, to ALWAYS return calls and emails in whatever you see as a timely manner, that's fine. But it's wrong to impose these on someone else because what you're not doing is taking THEM into consideration. Others' lives may be much more complicated than yours. When you won't consider that, you can't really talk about common courtesy.