That’s a very good point – there is not currently a check in place to catch this and I’d definitely encourage you to add a request here:
https://tribe.uservoice.com/forums/195723-feature-ideas
Something worth considering though is that – even supposing a check was in place – the strings of text making up each part of the venue (or organizer) would literally need to be identical. An extra space between a house number and street name, or minor typo, would throw this check.
Fuzzy matching to catch this would be quite an involved thing to develop and probably is the domain of third party extensions.
With all that said, if you feel there is a strong case for this, bearing in mind the complexities and limitations, then posting it on UserVoice – where other users can add their support and help us to guage demand – is probably a good way to go.
Also, is there a way that when you delete a duplicate venue you can assign a new venue to all of the events that were associated with the deleted venue? Same question for Organizer.
I’m afraid there is not, again that could be a natty feature request well worth posting on UserVoice.