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Chris, Even though Google crawls more of the web than any other service, it has a metric it uses to determine which and how many links to show you in the tool.  It does not show all of your links, even though it knows better than any service exactly how many you have. Moz, does not crawl the web as deeply as Google but it does report on all of the links it finds.  Rather than attempting to index the entire web, Moz focuses on crawling the pages down to a depth that have an impact on search results.  If the pages it crawls have outbound links on them, those are the links that are likely to passing some amount of pagerank/authority to the page their pointing at.  Below that level, the quality/pagerank/authority is too low to be of any assistance to the page it may be linking to. So, where GWT links represent a sample of your total links, open site explorer is a tool designed to show you the total number of links that are helping you with your rankings. Other tools exist as well, and they use different crawl strategies and that present links based on different metrics.  I think the more you understand OSE, the more useful you will find it.

Tag pages can be valuable if they are unique and substantive. If your tag pages are all short like these then I would 301 them.  You also might be able to disable them in your content management system. I don't use tag pages.  Instead my blog has a homepage, post pages and hand-built category pages that are outside of the content management system.