Well....that's partially true. But....
When you go to your iPhone Settings>iCloud>Photos you'll have three options:
iCloud Library: super lazy mode
New photos: lazy mode
Shared Albums: diligent mode
So... the response you got above is true for Super Lazy mode (and I assume for lazy mode too, since I haven't used it). But if you use the Shared Albums mode you can actually create albums in your iCloud and fill them with photos/videos that will remain in the cloud even if you delete them from your device. You don't even have to share the albums, just create and fill them.
In the spirit of not being lazy, you can use ANY of the three modes and then go to your Mac and DOWNLOAD your content locally. It will also remain on your local hard drive even if you delete it from your iPhone.
If you're desperate and feed up with the cloud, you can plug your iPhone into your computer open Photos, iPhoto, Image Capture (or whatever they have now on those Windows thingys these days... if you use that) and import your content as if it was a digital camera. Then you can delete it from your iPhone and guess what... It will remain in your computer.
But the clue is stop being lazy.... and I speak for all of us.