iPads are definitely capable of showing closed captioning if you turn it on under Settings->Video. The trick is finding content that actually contains captions.
A small portion of the content on the iTunes Store is captioned - this content is clearly marked with "CC" icons. If you record and export video with EyeTV software, these files will also have the Closed Captions intact.
I don't use Android so I'll have to let someone else answer that.
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