One thing that I've heard a lot of is the idea that Microsoft has a lot of money, so MacBU should be able to do anything: port a Windows app, add a feature to one of our existing apps, etc etc etc. I've come to think of this as the Microsoft fallacy.
The Microsoft fallacy has the following components:
Most people take it for granted that money doesn't buy happiness. But those who subscribe to the Microsoft fallacy forget that there are many other things that money doesn't buy. Money doesn't buy more time. Money doesn't buy great developers with specific domain knowledge. (Money can assist with recruiting great developers, but it's not the only factor in that equation.)
Those who forget that money doesn't buy a lot of things also forget that we might not have access to that money. Don't get me wrong, we're not pinching pennies over here, but we don't have access to an infinite amount of money. If money did buy everything that some people think it does, we might not be able to buy it anyway. I had an allowance when I was a kid. Today, as an adult, I have a budget instead.
The Microsoft fallacy has one component that isn't exactly fiscally-related, although most of the supporting arguments that I see for it are fiscal ones. That's the assumption that Microsoft is, well, Borg: there's one central processing unit that makes all of the decisions, and everything is done to a single end. This is true, in that Microsoft as a publicly-owned corporation is attempting to make money. But this component never assumes that Microsoft is doing the same thing as every other publicly-owned company; instead, it is assumed that we have some big overarching nefarious purpose, usually with either Bill Gates or Steve Ballmer cackling somewhere. This component forgets that we compete with lots of companies, and competition has one great benefit for us as a company: innovation.
MacBU is a small piece of Microsoft. We're ~180 people, out of a company of ~70,000. I'm reminded of this every time I meet a new person and they ask where I work, which often leads into a discussion of software that I don't use and know nothing about. The conspiracy theorists will tell you that MacBU is kept artifically small because Microsoft as an Empire wants you to buy WinOffice. Microsoft has lots of money, so MacBU could be a huge group if it weren't for the big mean Microsoft man keepin' us down. This argument forgets that, while MacBU is a nicely profitable business unit, we don't have as many users or we're not as profitable as as other parts of the business, so we simply don't get as many resources as other parts might.
What surprises me about the Microsoft fallacy is that I haven't observed it being applied to other large technology companies that make a lot of money. Maybe it's simply that no other large technology company is quite as obviously ubiquituous, even if they are larger.