Emulator

I fear this task is a bit more complex.

tl;dr: 0x80000000 is the default mapping location of the SDK of pRAM.

The point here is that we shouldn't assume if memory translation is enabled or disabled, neither the mapping table. So a good UI would show you the mapped memory (with all kind of error states as "not mapped", "no physical range", "io"), but also the different physical ranges: pRAM, exRAM (Wii only, currently not searched at all), aRAM (not mapable by the CPU, but used as some kind of swap file), vRAM (a hack to use more memory for the default swaped region).
As those mappings are neither surjective nor injective, we need both views.

The current memory viewer displays virtual memory with lots of shared code of the CPU emulation. The memory searcher is looking only in the pRAM, and it returns the memory offset. I guess this is for performance reasons, as using the CPU emulation will likely need a few seconds. But IMO this should also be fine.

Memory fetching function of the memory view: https://github.com/dolphin-emu/dolphin/blob/master/Source/Core/DolphinWX/Debugger/MemoryView.cpp#L352
The searching function with the linear memory assumption is here: https://github.com/dolphin-emu/dolphin/blob/master/Source/Core/DolphinWX/Debugger/MemoryWindow.cpp#L373