The first generation Xperia phones actually did something similar. They kept the battery at above 90%, by charging up to 100% then letting it fall to 90% again before recharging it again. Much better battery lifetime than keeping it at 100%.
But lots of people complained that Sony had a lousy battery charger system that couldn't even keep the battery topped up. So to avoid the bad press they changed it and kept it at 100% all the time, like the rest of the manufacturers.