This doesn't really look to show any sort of domination by Bitcoin on Western Union in the least, it seems like more of a one time instance then full proof of domination by bitcoin.
This event will be followed in other countries, I'm sure when everyone knows the bitcoin then they never use Western Union services again. I think sending money by Western Union is troublesome and depending with hours of work when taking submissions.
As much as I'd love for bitcoin to become accepted worldwide and to gain traction mainstream, I personally doubt that it will ever fully happen. I believe that some developing / developed nations will use it and it will gain traction their but it won't gain world wide usage instead of FIAT. I'll without a doubt agree with you on WU sucking but people are still able to use FIAT without an issue so theirs that.
People don't like change, it bothers them.