A search for voltage reference LM385B reveals that most of its many versions come in either 3-pin TO packages or 8-pin SOIC/TSSOP packages. Very few are 3-pin SOT-23 packages. I was wondering why is this? Why have 8 pin packages where 6 pins are NC?
There are multiple issues at play here, actually. Die size, as mentioned, is one of them -- a SO-8 or even a TSSOP-8 can accommodate a larger die than a SOT-23 can, although modern references are available in SOT-23 packages these days (the Intersil FGA parts come to mind, specifically).
Other reasons include mechanical stability for high-accuracy references and the need to provide post-packaging trim access due to packaging process induced shifts in the reference voltage. LTC AN82 discusses these problems in more detail.