What are the really difference writing WordPress 3.x widget plugins?

As per your other question rather than trying to use older API to implement widgets it is better to use newer and current approach as per Widgets API in Codex.

The difference is that newer code is more reliable and more functional (allows to easily have more complex features, such as multiple instances of the widget).

So issues with your code example are probably not worth fixing, better to just move to using currently suggested way.

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