Well, that depends. The battery reports voltage to the phone. The phone reports how charged it is to the user. Each device could define 100% differently. It's possible that the iPhone allows the battery to reach a higher level of charge (higher voltage) before considering it "charged" than the typical Android phone. Not saying that's the case, just that it's possible the charging calibration is different.
Pretty much spot on there.
The Android system doesn't necessarily get more efficient, nor does the battery fare better when drained, HOWEVER, the system monitors the full/empty states of the battery, and calibrates the battery %.
As far as leaving it plugged in for a whole month, no harm, no foul. Modern devices (~10yrs) with Lithium Ion batteries, have circuitry that prevents over charging, which could have explosive results. When it reaches what the circuit says is the batteries max, it stops charging. Usually when it gets down to 97-98% or so, it'll charge back up.
That sounds like it would be bad... but it's really not, and cumulatively is no different than running your phone down to empty (again the circuits will prevent it from reaching a critical point that will damage the cells).
In a nutshell, the batteries have a "charge cycle" of 100%. If you use 25% one day, 50% the next, 25% the next, with a full charge in between, that's actually a SINGLE charge cycle. Same with draining it 1% 100 times. or 1 time 100%.
Don't believe me? The following link from a reputable (although possibly hated company around here) explains it pretty clearly. :-D
Even though it's from that reputable company, the battery technology is NOT proprietary to them.
Batteries - Why Lithium-ion? - Apple