Database Count / License - Should be quick

I'm setting my Exchange 2013 deployment up according to the EX2013Calc5.9 spreadsheet (which is brilliant by the way). And with all my given input data it said that I should use 6 Databases with 35 users per DB.

Standard can have 5 active / passive DBs. So my question is why did the calculator think this was better, and can I just use 4 DB's in liu of 6? Whats the rationale behind that aside from DR. Which they are still on the same logical volume.

Thanks!