why do watch ads all display the time 10:10 ?

[Diana Lory]

[tro]

interesting, I must pay attention next time I see any watch ads, it never occurred to me to even look

[G. Whilikers]

Part because it's symmetric and looks nice, part because it lets the watchmaker's logo be seen.

[Monu]

It's all to do with marketing. Clock and watch designers commonly put their brand name directly below the 12 on a watch face. Positioning the watch hands at 10:10 creates a wedge that draws the eye upward, displays both hands and, most importantly, showcases the brand!
The consensus of opinion (some internet references quote this as confirmed by Timex) is that clock and watch hands in advertisements are typically set at 10:10 so that the company's logo will be well-displayed.
Watches in advertisements and in shop windows all have the time of 10 past 10 because it creates a smile-like shape. 10 is a feel good number- so 10:10 leaves one feeling warm and fuzzy and lucky. This attracts more customers as the watch looks "happy".
Actually a French clock-maker asserted that all the clocks were set at 10 past 10 to honor the memory of the Sun King, Louis the 14th who was, he said, beheaded at that exact moment which is obviously wrong since that very king was not beheaded, but affections remain high for this king who loved clocks so much that he turned the royal clock-makers into aristocrats, noblemen.