The answer: it depends. (Surprise)
Just because various software vendors don't invest in cross-platform software development doesn't mean you can't migrate to a new platform. COTS doesn't necessary mean vendor-locking, FOSS doesn't necessarily mean vendor independence and open standards.
This is the nature of competition between Free Open Source Software (FOSS) initiatives and established Commercial Off-The Shelf (COTS) Software manufacturers. Executives are faced with immeasurable intangibles and difficult decisions for IT investment. There are many ways to crack the puzzle. Here are 5 important things to ask yourself:
Ease of Integration: Open Standards - do you need the solution to be flexible and have ease of integration?
Flexibility and extension: Do you predict a need to extend internal components or extend the core product?
Supportability - do you have internal IT operations that need to support the solution ? Do you have skills in-house to support and diagnose?
Cost - does it make sense to buy a product versus the support costs of FOSS?
These are a few factors that need to be evaluated. Solution architecture evaluations require a deep dive into specifics. ATAM(tm) is a framework for architecture evaluations that I have used, I plan to get certified and use it officially in engagements in the future. It is a valuable guide to generate a Utility Tree and evaluate Quality Attributes. More to come ....