Yep, I work at 100dpi for the 1 inch=1 square maps. This is down to a couple of factors - many of these started life as print maps - so you have a 300dpi single page map inside a product, and a 'full zoom' map for home printing at 3x the size at 100dpi. That balance works pretty well for a lot of battlemap maps. The second reason is that I started down this road using vtts and for them, 100 pixels per inch is a good standard. At full zoom that image will be 1 inch on most screens.

Finally it's a matter of cost - for the money these make, there's a limit to the amount of time they can take. 300dpi at full zoom takes longer than 100, so I stick to 100 for the sake of my own sanity!