The difference between WS2811 and WS2812

I've been starting to work with a 5050/PLCC-6 RGB LED that is usually called WS2811 online, but sometimes called WS2812. It's a fantastic LED that is very bright and has the constant-current driver chip built in to the actual LED. It takes three inputs: 5V power, ground, and data in. Each LED takes 24 bits (8 bits for each color channel), then buffers and retransmits the rest of the data stream to the next LED in the chain.

At $0.14 per LED plus driver chip, this is incredibly cost effective, especially compared to the TLC5940 chips I usually use. The PLCC-6 form factor is easy to solder as well.

So, why are the LEDs sometimes called WS2811 and sometimes WS2812? The datasheets make this pretty clear, but here's the answer in picture form.

The WS2812 is the LED with embedded driver chip. The LED is 5mm x 5mm, but fortunately I have a USB microscope:

The driver chip is the WS2811:

It also comes in DIP-8 and SOP-8 packages if that one is too small to work with.

Datasheets: WS2811 (rar), WS2812 (pdf)