From the other comment, it is completely equivalent, and I will admit that the pipe is due purely to my ignorance. I usually use `sort` for sorting the output of other commands, and so I forget that it can open a file on its own.
Don't worry about the cat it does have a purpose: portability.
cat in.txt | sort > out.txt
works in powershell(cat is an alias for Get-Content and sort is an alias for sort-object)(without the sort it wouln't work).
Aiming for succinctness by using aliases and using redirection instead of cmdlets for writing the file (shorter, but less flexible):
That's not code anyone should write outside code golfing, though ;-)