Both Lua and Ruby are optimized for aesthetically pleasing syntax that is easy to parse for humans, even for people new to programming. I think "end" works better for that goal than curly braces which most people don't even know how to type and that are rarely used in English outside programming.
Personally I vastly prefer keywords to special characters. My brain has more trouble parsing symbols than words. I have real trouble reading mathematical notation but if I see an algorithm written out with words I am able to grok it quite easily. I think lot's of people are the other way round, not sure . Might be because I was a heavy reader in my youth.
That said I switch between C-like and Lua/Ruby style syntaxes back and forth all the time and it is really not an issue.
Reminds me of when I first started out and would put a comment on every closing bracket of the context of what started that bracket.