As see this it is simply not true. First you can import images as much as you want on any platform. Droping an image into the text of a tiddler will both import and link to it, or drop it else where to import it then reference as needed.
Then there are a range of ways to subsequently externalise an image, in someways as I understand it it is automatic with node.
I use single file wikis a lot
I like/have a batch exporter tool that turns images into external ones and gives me a zip file of images I can save in the same or selected folder below the single file wiki. I just need to do this occasionaly before the wiki gets too slow to load.
I will share if I can find it. Yep, here it is Externalising Image Files with JSzip using tools you probably already have