i think everyone hits the button by mistake at some point, i did when i used a mx518.
there is no benefit to having it on top. no one uses it. you say many people, find me ONE?
zzz
It's better to remap the DPI buttons into additional weapon and or item slots. Plus more buttons doesn't hurts lessens the need to spider walk across the keyboard to reach some bind that is hardly used or is often can be quicker to access.
Either way it's pointless to switch DPI on the fly, makes you lose consistency. Too many people think DPI is merely a speed modifier like an accelerator on a car.
Ironically many of these same people maintain the same or almost the same sensitivity and don't use calculators to compensate for the higher DPI since it does increase the speed but at the same time read's movements are far smaller intervals thus accuracy. And not just from the higher DPI but also the reduction in master sensitivity.
As for the MX518 well considering the 518/5 used similar locations. Now a days Logitech has offset the DPI buttons to different locations like on the G500/700 near the primary button on the left hand side. But I find it hard to believe they are that easy to hit considering how small, resistive, and recessed the buttons are usually on the 518/5.