If it's a sealled cabinet, then foam would help the cab/speaker reach a lower frequency response. They routinely use fiber insulation-like materials in the audio industry to improve bottom end performance of sealed enclosures. It's a way to make the cabinet respond as if it's a larger (cubic foot wise) one.
I personally like sealed enclosure for home audio because they tend to have a much more level bass response... Ported enclosures can get hit somewhat lower frequencies, but they will not have as level of a response.
But for musical instruments, I don't think I would worry about what the audio industry is doing to much. Musicians MAKE the sounds, audio equipment tries to DUPLICATE it.