The 10.8v figure assumes you get 1.2V from each of the 9 NiMH cells while under load. It's just a rough figure that most people use when talking about different setups. The 12.6V sounds like it's assuming you have 3 Li-ion cells which are normally charged to 4.2V each for a full charge. In reality, the actual voltage you see from the stack of 9 cells will depend on a lot of factors: charge state, cell temperature, current being drawn from the cell at that moment, etc. You may very well find that the entire 9 cell pack fresh off the charger is 12.6V, but once you start drawing roughly 3.25A from the cells to feed the 1185 bulb, the voltage will drop somewhere closer to 10.8V. The more freshly charged the cell is, the higher the voltage will be. Also, the warmer the cells are, the more easily they can supply power so the voltage will not drop as much under load. That is why people talk about the risk of instaflashing their bulbs when using a light immediately after charging. The batteries are at their highest possible voltage and the cells are still warm from the charging process. When you couple this with the fact that an unlit bulb is cold and thus has lower resistance, you end up with a higher voltage across a lower resistance which will give maximum current which may blow the bulb. Once you turn it on, the bulb filament heats up and has higher resistance which reduces the current flowing through it. Personally, I have never had a problem blowing bulbs but it really depends on your setup. I just use "normal" mods like the Kiu sockets and Energizer AAs. However, if you use batteries like the CBP1650s that have very little voltage drop and do some of the resistance lowering tricks on the switches and tailcaps, you might need to let the cells cool after charging to prevent instaflashing. Personally, I don't think squeezing every last drop of brightness is worth the risk. I want a light to use whenever I need it.
