Hi Titan -
I'm not an SEOMoz employee - so I can only speculate here.
From the blog post on Raven Tools - they made the comment that the reason they decided to stop offering the rank tracker is because they failed an audit for the Google Adwords API. Google gave them an ultimatum - either stop using scraped data, or lose access to the API.
From what I understand, SEOmoz was recently faced with the same problem, and they chose to drop the access to the Adwords API, instead of giving up access to the scraped data. This is understandable, since SEOMoz's tools focus exclusively on SEO - while Raven offers a a wide range of services - some SEO, some PPC, some Social Media, etc.
So, I would be surprised if SEOMoz would stop offering the rank tracker. Though I really have no inside knowledge about this at all.
I think the SEOMoz rank tracker is an internally developed tool. Raven tools, and a lot of other SEO tools in the industry used a company called Authority Labs.
http://authoritylabs.com/
Rank tracking is the only thing that they do, and from what I've seen, their data is a bit better overall, if you're just looking for rank tracking. They also do daily monitoring of keywords, which is a bit overkill from my perspective - but could be useful if you're in a very competitive niche.