Canon claims that EOS 6D has special capability to focus in low light, but it has only one cross-type sensor and overall only 11 focus points. Does only one cross-type focus point in the Canon EOS 6D affect its ability to focus in low light? Is it correct to assume that more cross-type focus points produce more accurate and sharper focus?
As with many things, the marketers have tried to convince us that bigger, more, or higher priced is always "better". Most of the time in photography quality trumps quantity.
Regardless of how many focus points a camera has, the camera's system primarily uses one to actually focus the lens. It may be a single point manually selected by you or it may be one of several AF points that are active based on the selected settings. If you have multiple focus points selected and more than one light up in the viewfinder, it only means that the camera is telling you that all of those focus points are at roughly the same distance.
What is more important than how many focus points the camera has is how sensitive the focus points are, and how accurately the camera/lens is able to move the elements in the lens to match the instructions from the camera.
Here is a real world usage quote from Brian at The-Digital-Picture.com in his review of the Canon EOS 6D:
A cross type sensor has the ability to focus on both horizontal and vertical patterns, but that in itself has little effect on the ability to focus in low light. What matters there is just how sensetive the sensors are.
Most things that you focus on have a combination of vertical and horizontal lines, so any focus sensor can handle those. Cameras generally have a few cross type sensors to handle the special situations when you focus on something that has only horizontal or only vertical lines.
A cross type sensor is of course more complicated to build and thus more expensive. By having only one or a few cross type sensors, the manufacturer can use more sensitive sensors without adding too much to the cost, so indirectly it can allow for better low light capabilities.