the flowers are on the TV. This is correct. If they were on TV you'd be watching them.

When we talk about most forms of entertainment we usually use 'the'. For example, we say: 'I am going to the cinema.' 'I was listening to the radio.' 'I like going to the theatre.' When we are talking about television we usually omit 'the'. 'I like watching television.' However, sometimes we do use 'the'. 'What's on the television this evening?' and 'What's on television this evening?' are both common. When we talk about all the above forms of entertainment as professions or art forms, we usually omit 'the'. These are examples: 'Cinema and television are very different from each other.' 'She has a job in radio.'

Ok, so it's not a mistake. The example with flowers is different - we're talking about the TV set in this case. Thank you, Naga!

You could say either 'There is a funny advert on the TV' or 'There is a funny advert on TV'. I would say the second is more correct but both are used. When you refer to a specific TV (like your TV), you definitely need the article: 'Don't put the flowers on the TV.' 'Radio' is similar: We say, 'I am listening to the radio' rather than, 'I am listening to radio.' Some issues like this are simply matters of usage and idiom rather than grammar.