That is not entirely correct if you’re using the regular version free of moisturizers.
These brands are notorious for leaving films because they add skin moisturizers.
- Palmolive Ultra Soft Touch
- Dawn Gentle Clean
- Ivory Classic Dishwashing Liquid
This particular version of Palmolive as an example advertises the exact opposite.
This is why its important to read the label.
Just to explain why I know this stuff—quick, funny story! I was a volunteer leader at a youth group, and we were hosting a charity car wash. Mid-morning, we ran out of soap, so in a pinch, we dashed into the supermarket (which was kind enough to let us use their parking lot) and grabbed some Dawn Gentle Clean. I mean, all soaps are the same, right? 
Yeah, no. We found out the hard way when we couldn’t get the car windows clean! Back to the store we went, and the manager kindly explained the differences in soaps and pointed us to a better option. You live and learn! 