Just an update if someone else is looking through community before checking Dell Drivers 😉
Latest version of the touchpad driver (Version 8.1206.101.118,A08) has the "Reverse Scroll Direction". Funnily enough, now the default scrolling for two finger gesture is "normal" and by selecting the "Reverse Scroll Direction" you get this OS X type of inverted scrolling that myself and others in this thread are so displeased with.
Another funny thing of course is that this computer came off-the-box Jun-2015 with the old (2013) touchpad driver, but that could be due to our procurement process too.
So, this fixed the problem for me (E7240). Thanks to Dell for listening user input and updating the driver so it works as any Windows user is expecting.
InvertScrollFlag does not appear in my list of fields under HKEY_CURRENT_USER\Software\Alps\Apoint. This is a Dell Vostro 3550 laptop which has been in a box since new, and way behind on updates, so I'll try that and see if it helps. For now, I feel like I'm up the creek with a set of oars, and not a paddle!
I have the same screen and there's no reverse-scroll anywhere; however this is from a factory reinstall where I used the Dell Update Manager instead of just Windows Update, and the previous install (where I used Windows Update first) gave me the option.