100' wire in the wall will be a 'solid' copper rather than thin gauge 'stranded' which gives greater flexibility but not ideal for carrying the same amount of current. the 100' coiled up in your extension reel will also heat up, so better off lying on the floor!
Not sure solid versus stranded makes for a valid argument. First off 8 gauge or bigger wire (smaller number) is usually stranded, even in walls. Second, IIRC, good wire strippers have a solid and stranded label for the same hole because stranded is a bit bigger.
One thing that does surprise me, I would have thought that all the hose reel companies would state that you should always unreel the whole spool, but I don't think they do. Should be only a concern when pulling Max amperage for a given guage, but companies being afraid of liability and lawsuits, figured they would all specify this warning.