The package is here: http://www.nintendo.co.jp/support/oss/data/MarioKart8_OSS1.0...
(It's the same principle that allowed Apple to include GCC with Xcode before LLVM came along.)
The are also exceptions for libraries provided by OS. (Which is why you can GPL code on Windows which links a proprietary libc from Microsoft).
Apple gets away with calling GCC because it's a different application being invoked by it's natural interface in the same way that Xcode invokes git internally. (And also why people use the libgit2 project when they need to call git as a library which licensed under LGPL with the classpath exception).
Now LGPL is an entirely different story. LGPLv2 was intended that you be able to replace dynamically linked libraries in an application. The changes you made the library must be open sourced and I should be able to replace that library as a user.
In theory you satisfy the requirements of the LGPL license if you wanted to statically link though if provide the objects and archives of your code if you wanted to statically link with LGPL code, but doing this was not really well defined in the license as valid. In LGPLv3 they clarified this is totally valid and allowed.
The interesting thing is that LGPL was a license best written for C libraries at dynamical library level and breaks down in a few cases for different languages. It also breaks down where you have inlining and code getting embedded from headers that would break the ability in some cases for you to be able to change the library and relink. Implementation details of vtables, etc can get embedded too that would make it impossible to change the library.
This is why during the GNU Classplath project (to replace the Java Classpath before Java went GPL anyways), they added the "classpath exception" to GPL itself instead of using LGPL. See here for details: https://en.wikipedia.org/wiki/GPL_linking_exception
This and other "how long is a piece of string" type of issues is why I think licensing is overall a horrible ridiculous convoluted mess.
I would however call it a bad bet to incorporate someone else code into a proprietary product, on the off chance that the general known line of "linking" can be invalided by the courts. The lack of case files should be a strong hint towards that.
However, the SBC codec library is LGPL, not GPL-only. Notice COPYING.LIB along the COPYING!
Just the main sbcdec and sbcenc are pure GPL, and they are not very long files, so it's likely they rewrote those parts.
http://www.gnu.org/copyleft/gpl.html - "And you must show them these terms so they know their rights"
If they were distributing the binaries without any indication that they were GPL'ed (i.e. no written offers), then yes, it would have been a violation. But it's not a violation any longer. They seem to be under compliance.
Same pattern as how they handled Game Cube compatibility on the Wii, I believe. I wouldn't be surprised if Wii mode on the Wii U were similar, but I'm not familiar with that.
Source: I'm a Dolphin developer.
Keep an eye on the work MrBean has been doing to MarioKart8 - http://www.youtube.com/user/MrBean35000vr