I change songs all the time...
1. The overwhelming majority of music on the web is stuff that someone just figured out, or has already been altered to make it sound "better" on a ukulele. If you use music from the web, you really have to just trust that whoever put it there actually knew what they were doing. (Most don't...) It might sound good. It may even sound better. Most of the time it really doesn't.
The same problem exists in some ukulele song books for legal reasons. In order to print original music that isn't public domain, permission is required from the copy right holders. People get around the restrictions by intentionally altering the music just enough skirt copy right laws. There are versions of songs that have been altered because some artist or another changed the key or lyrics to make it their own, so those versions deviate from the original work. When you have several versions of the same song by well known artists, there's a chance that every version is under copy right, so often even the previously altered versions have to be altered in order to print the music.
2. Then there's the difference between most instruments and ukuleles. An acoustic ukulele doesn't have the same resonance as most instruments, which is why we learn strumming patterns or learn to pick out the notes.
3. I have a fairly limited vocal range, and since I only play songs I sing to, sometimes I choose one version of a song over another so it doesn't freak out the cat. But also, singer/strummers use a version of chord melody that doesn't really follow the same rules as someone who just plays. Singer/strummers have two instruments (our instrument and our voice), and as long as we can sort of harmonize the two, we can play a little fast and loose with chord structure a bit. One of the things that really amazed me when I started on the ukulele is the number of of people who play, but don't sing... If someone is picking or strumming without singing, they have to be a lot more precise.
Really, there isn't much choice in the matter unless you're reading actual sheet music instead of chord sheets or tabs. Timing is everything when you play tabs, and changing a strum pattern can change the entire meaning of a song. With all the variables already in play, I reckon that I'd rather try to make my music mine instead of trying to play exactly like someone else.