Thanks for all the considered responses, which I've enjoyed and been appalled by in equal measure! 
We have had 'The talk' - but my wife likes to see blue liquid in the toilet bowl. She doesn't have the same concern for the environment that I do.
...have a message for your wife - LTB! 
I think the blocks are just staining the crust formed by urine resting in the bowl, like disclosing tablets and plaque on poorly brushed teeth.
No, it's not that. I get my hand down the toilet on a regular basis - my poo on the side of the bowl, my responsibility. It's only the combination of wee and cistern block that creates the crust.
clean it yourself! See above.
Maybe you could pee in a big jar? One with a lid. Then empty in the loo when you are prepared to flush it. Your wife will probably want you to keep this jar away from anything else, garage or shed perhaps? It'll save your loo and you won't need the blocks.
This is the point at which I repeat my recommendation for Method toilet cleaner. It's environmentally friendly, smells of peppermint (so no nasty loo-cleaner smell) and best of all, actually works on limescale. I live in a really really hard water area, and left to itself, the loo goes black under the waterline in days. It's revolting. I have tried every loo cleaner under the sun, including blocks, and nothing really works apart from Method. It's amazing.
I like the jar idea - I could tip it down the sink! And I'll look out for Method, thank you Annie.
I'm with you OP - we follow the the mellow yellow approach & it is fine for me. We also don't have blocks in the cistern, which are dreadful for the environmental & utterly pointless.
However, in the the whacky MN world I am apparently a minger of the highest order - the obsessive hygiene of some posters on here is unfuckingbelieveable to me.
We need a 'Thumbs up' emoticon - for that post and many others.