Why would an OPA705 come shipped in a moisture proof package with dessicant and a moisture indicating tab?
I can see ESD protection and maybe a lack of moisture protection becauses ESDs are prone to occur when dry, but why moisture protection?

 

Probably due to concern about moisture diffusing into the package and causing problems during assembly - which may or may not be as much of an issue for your planned method of assembly, compared to industrial methods such as infra-red reflow.

http://en.wikipedia.org/wiki/Moisture_Sensitivity_Level

 

It is to maintain the device in a 'like new' condition during extended storage(like a supplier who stocks items for you to buy)

Humidity cycling, just like temperature cycling can create problems for the electronics plastic and metal interfaces. The manufacturer requires these measures in order to 'guarantee' the devices operation after a set timespan of many years in storage.

 

Slows oxide formation on the pins.

 

That's a lot of effort for a $0.75 chip that is not visibly different from any other DIP8 part I have. Datasheet doesn't say anything about that either.

 

All depends on where its coming from/where its going/what requirements that manufacture is bound to comply with,etc...