There are many Jellybean users(including me) who do not get an option to download offline voice recognition support in Google Search app(see image below).
The only explanation I was able to find was that Google excluded some Jellybean devices to download offline files due to hardware limitations(Source: utter! FAQ)
I don't know what the limitations are but I found a workaround, and here it is!
The Google Search app downloads the offline voice files in /data/data/com.google.android.googlequicksearchbox/app_g3_models/<language name>/<offline voice synthesis files here>
To trick Search we just have to place the offline voice files in the directory and set permissions, and you'll have offline voice available on your unsupported device
(See next post for offline voice files download)