1. From the beginning it was known that simple numbering system for snapshot (commit) names would not work without constant access to single central 'numbering authority'. So the history of git is without this meandering; on the other hand git had example in Monotone, existing distributed version control system. But this is certainly minor issue.
2. The staging area was not created to be able to split changes into more than one commit or keep dirty files in working area (with changes which do not go into snapshot). This is side benefit, and something you should not abuse. The main reason behind staging area is merging. This is IMHO fairly important didactic issue.
3. Git calculates SHA1 of uncompressed object, and then uzes zlib compression on it, not vice versa as it is said at the end of "The Git Parable". It used to be the way described (first compress, then SHA1 of compressed contents) for a very short time and was abandoned; current way allow to transparently improve compression.