The difference is that the Samsung Series 7 Slate and the Surface Pro both use Intel Core i5 processors, and a more traditional PC architecture, while the Atom processor used in the Dell Latitude 10 is a SoC (system on a chip) that merges more functionality into less space. It's possible to get a Windows Pro tablet that weighs roughly the same as a Windows RT equivalent, but if you want the processing horsepower of a true Intel Core processor, your tablet will likely weigh a bit more.
This is where things shift in favor of Windows 8 Pro tablets. The meat and potatoes of why you'd elect to invest more money in a heavier, louder tablet with inferior battery life: it runs all software. Windows 8 Pro behaves the same whether it's on a desktop, laptop, or tablet, and all of the software you rely on when using Windows will work on the Windows 8 Pro tablet.
Windows RT can only run apps specifically developed for the Windows RT Modern (formerly known as "Metro" interface). The volume and quality of apps available is underwhelming, but growing rapidly. However, that won't do you any good if you have a customer tracking tool, inventory management software, or some other industry-specific application that only runs in the full Windows operating system. The difference, again, is that Windows RT is strictly for ARM-based processors, while Windows 8 Pro can be used with x86 processors.
Another area where Windows RT is no match for Windows 8 Pro is when it comes to the more advanced features and capabilities of the Windows 8 operating system. A Windows 8 Pro tablet can join a Windows network domain, and be managed and monitored just like any other Windows PC. Windows RT cannot join a domain, and is limited to rudimentary management through Exchange ActiveSync or Microsoft System Center Configuration Manager.
Aside from joining a domain and/or being managed through Active Directory and Group Policy, though, an x86 architecture tablet running Windows 8 Pro or Windows 8 Enterprise can encrypt data using BitLocker. A Windows 8 Enterprise tablet also opens up a whole other realm of possibilities, including Windows To Go, DirectAccess, AppLocker, BranchCache, and other Microsoft technologies that are not available for Windows 8 Pro--never mind Windows RT.
The Samsung Series 7 Slate doesn't have the cool Touch Cover like the Surface RT, but it does have a docking station. When at my desk, I just snap the tablet into the docking station and use it like a traditional PC. I have a Bluetooth keyboard and mouse, and the dock connects the tablet to my monitor via HDMI, and provides a wired ethernet connection and an additional USB 2.0 port. Dell offers a similar docking station for the Latitude 10 tablet. In fact, most Windows tablets have some keyboard docking option.