Huh? The iPad is pad-shaped and "pad" is a commonly-understood noun in the tech world to refer to these devices.
Same thing for iPod. It's pod-shaped (or was when it was introduced) and it's a pretty simple mental leap to classify this "pod" as a thing that you put your music "into".
By stark contrast, "Qwikster" has absolutely no mental, cultural or conceptual link to the product or service it describes. It's worthless as a name in addition to being confusing, already taken by various other services, impossible to spell, and dorky.
Oh I'm sure I could rattle off at least a hundred or so names of products and services that have no relationship to their relative products, are challenging to spell (assuming you hadn't heard of them before) and sound somewhat similar to other services.
iPhone? Sure. iPad? Maybe. iPod? Definitely not.
It only seems that way because the iPod dominated the product category so strongly as to become synonymous with "portable digital music player."