Yes, it's normal for the rate of blocks being received to decrease as the download progresses.
The reason it slows down is because there were very few transactions in each block in the early days of Bitcoin, so the blocks were smaller. Later blocks are bigger.
The Satoshi Bitcoin Client is still a Beta version, and even if it wasn't it may still need to download the entire blockchain which I believe is over 2GB.
Which platform are you running the client on? You should be able estimate how much data is left to download by looking at the blockchain files on disk in the application folder.