They had a problem of not offering a kit for P&S superzoom upgraders. The original SEL18-200 is way too expensive and large for that purpose.
So they simply add a cheap Tamron-based superzoom and are now able to offer a good enough relatively cheap kit.
Good point agorabasta. Here is the quote from Amateur Photographer
Costing £670, the new 18-200mm will be £30 cheaper than the existing version. However, it does not offer the same level of image stabilisation and its minimum close focusing distance is 30cm, compared to 50cm on the current model, said Asai.
So why would anybody (other than those craving the Sony name on the lens) spend £670 on essentially a Tamron lens when you can buy the Tamron on Amazon UK for £500 delivered? I think that David Kilpatrick quite likes his Tamron 18-200 for NEX.
Not sure Tamron will appreciate the comment that their image stabilisation is less efficient than Sony's own. Maybe reviewers can pass a verdict here.