[ moved from the Acrobat forums to InDesign ]
That's only an issue if you are printing using Black ink only. Preflight presumes that you are going to print on a press where you have only CMYK and Spot inks available, so your RGB images would need conversion at some point in time. That conversion can be done before placing, during export, or in the Printer's RIP. This makes it not terribly helpful for RGB workflows as it won't differentiate between RGB conversion and "real CMYK" when looking at the sparations (plates) that would be generated.
Below that check is one called Color Spaces and Modes Not Allowed that you could use to flag anything that's really in CMYK, but this is going to generate even more "errors" since everything defined as [Black] is in CMYK mode. It is safe to ignore those warnings, too, unless they apply to an element like a graphic or image that must be RGB (this is really the only way I know for Live Preflight to kick out warnings about CMYK images in an RGB workflow). The old preflight is still there (the first screen in File > Package is really the old Preflight), and it will list images, along with their color spaces, but won't tell you about native objects created in ID.
The bottom line here is if your printer asked for RGB images, that's what you should send. All will be fine.