The store was originally a native app for the first couple of years. Whenever the Ribbon UI went to the one with sparkles, the store went to a crappy web UI that was unbearable to use.
I love seeing bits and pieces of the original UI that were clinging on by necessity, namely the firmware upgrade screen. It was likely made immutable at the cost of UI updates.
Kind of the story of everything - responsive native app replaced by clunky web app.
It seems sparkles were added in 3.0 FW in 2009, while store was replaced in 2012.
I think FW update splash is not running the full OS and it only displays static image for simplicity, XMB never used static image as background.