Cross-selling and up-selling based on product line extensions is prevalent in industries that have rapid product lifecycles.
The third major factor to consider in brand extensions according to the
Marketing Leadership Council (2005) is the need for infusing the existing
brand with additional publicity and greater exposure. The Hummers' product
line extensions to the H2 and now the H3 Models underscore both the extreme
durability of this vehicle yet also give General Motors an opportunity to
further clarify their branding message of the Hummer line of vehicles also
being safe for families. Their extension from being a rugged off-road
enthusiasts' vehicle to that of a vehicle...

In reality there are many more factors in addition to those briefly described, and as product lifecycles across
many industries continue to be shorted, the need for having a solid brand
extension strategy in place is critical.
Sources:
Marketing Leadership Council (2005) - Leveraging the Parent Brand in the
Introduction of brand Extensions. Corporate Executive Board Publication.
April, 2005. Pages 3, 4, 13.