In my experience in IT in support and administration, I have not found it to be the case that it is only an "exception of a niche few professionals who are dependent on Windows" (spelling corrected). It would be nice were that the case. Unfortunately many professionals are forced with the decision to use big name, industry standard, efficient (for their processes/business), well known, well supported software or to have to spend that time and money reinventing that wheel and doing so imperfectly.And I disagree, with the exception of a niche few professionals who are dependant on Windows and it's associated, expensive, software; the open source look alikes work just fine and will achieve everything they want and need - As an example, as an amateur photographer and someone that needs software to resize, crop and add layers to images for my various online business needs I found Gimp to actually work better than Photoshop - In my scenario.
They may work with document management systems with built-in databases, reports, forms, and automation. The database stored in Microsoft SQL Server presents in Microsoft Excel using a combination of add-ins, MS Office Interop assemblies, and .NET programming. It does a lot of the work for them on linking to other workbooks, updating the numbers, calculating and adjusting calculations, and pulling in information from prior years. They have programs that ask them questions and output the answers to properly formatted forms in Microsoft Word documents or Microsoft Excel workbooks.
A third party provides the research and keeps the forms up to date with any changes that happen multiple times a year. When the updates do happen, the data persists and the form updates underneath it. This is again accomplished by in one case add-ins to Excel and Word and in another through a Microsoft SQL Server back-end with a .NET developed client that outputs to Excel/Word using Interop assemblies and Office add-ins.
A big name statistical sampling software they use can pull information from PDF files, perform statistical analysis based on criteria they specify and output the results to Excel. This saved them from having to OCR or convert the PDF to a spreadsheet program (and deal with the imperfections of that process), manually group, format, and perform calculations on the spreadsheet to get it into a usable format.
Their time, billing, expense, and reporting software is Windows only. Their scheduling software requires Internet Explorer (even though it is browser based). Their CRM is only feature complete when used in combination with Outlook and Adobe Flash (bleh). You can import from and export to CSV if you don't mind having to manage synchronizing manually.
They are at a competitive disadvantage if they don't use the software. They are not developers and work for a medium business. Big businesses can afford to hire their own developers, create their own software, employ their own compliance and research teams (I'm speculating here). Individuals and very small businesses may not work with the sort of complexity that requires this sort of investment in software.
Some of the vendors that I deal with are just now starting to move in the direction of platform and browser independence. At the moment, their efforts are mainly aimed towards allowing customers to view data from any device or are on a go forward basis (you need Windows to view prior year or archive data). However, it is hard to see some of the products being able to achieve independence from Microsoft Office. It's not in their interest to have to create their own online, web based "Office Web Apps" for the products that are web based. It's hard for me to see the thick client or client/server program vendors being able to cut out the interop/add-in integration with Microsoft Office, given what it does and the seemless functionality their customers have come to expect. Currently, most of the users I support have no idea that when they are working in Excel their data is actually in a SQL database for some of their workbooks. They think they are making changes in Excel.