NXT single address per user vs bitcoin single address per transaction
It's not hard to use Bitcoin approach in client software. NRS (Nxt Reference Software) doesn't support this because anonymity is not ensured this way, it only creates a delusion of anonymity (http://people.csail.mit.edu/spillai/data/papers/bitcoin-transaction-graph-analysis.pdf). CoinShuffle (http://crypsys.mmci.uni-saarland.de/projects/CoinShuffle/coinshuffle.pdf) will be added to Nxt soon to provide a better protection against deanonymization.