Unless if you wanted to understand manzai owarai or Japanese stand up comedy, I believe learning the standard language is enough to understand the normal Japanese shows. I ruled out the statement that most celebrities come from Osaka but a lot of comedians do.
In some normal Japanese shows, occasionally they do use Osaka-ben (Osaka dialect) to be funny even though they, themselves, don't even come from Osaka. However, the Osaka-ben they used are the simple or commonly used ones that even anybody who's not from Osaka can understand it. It'd not be a problem once you've mastered the standard language.
I reckon this is true for any language with many different dialects. Even in my country, people from different states have different dialects. I can understand the simple or most commonly used ones but not when they started talking in full dialect. That's when it'd start to become rubbish to my ears even though it's essentially in my own language.
I gathered that that person who told you that learning the standard language won't be enough to understand Japanese TV shows meant that in the TV shows, they don't speak like what you learned from textbooks. Neither does any of the other languages in the world I believe. So you have to learn the spoken language, slangs et al. by either living in the country itself, read a lot of manga (and if you don't understand, ask your sensei or in a forum) etc..
For example:
1) Commonly used Osaka-ben:
めっちゃめっちゃカッコイ (extremely cool)
>>めっちゃ (slurred Osaka-ben)-->めちゃ(osaka-ben)
>>that is often heard right?
2) Spoken
おすすめの店があんだよねー
>>あんだ (col) → あるのだ
Conclusion: I seriously don't believe that Japanese TV shows are heavy with Osaka-ben unless you're talking about comedy shows/manzai/local Osaka shows.
Ok do take this with a grain of salt ;)