Why would you assume that immediate translations are only useful when out and about? People talk to each other while indoors too! Very disappointed it's not included for the iPad.
Hopefully it will be added there since it makes sense to have it there too. That said, seems like the native Weather and Calculator apps never quite made it to the iPad, so you never know.
i suppose they figure you can listen to it if you want to know the pronunciation. But having the pronunciation written our in romaji/pinyin can be useful, if you want to learn how to say it yourself.
On another note, I found that if you set it to "translate" English to English, it'll basically transcribe what someone is saying. Could be useful for deaf/hard of hearing people.