There's nothing hyperbole about it. Have you thought of the reasons why people won't go looking outside of MAS? It becomes more logical and clearer.
A lot of users are lazy, some are less technical, and users often fall into both categories
If they can't find it on MAS, then the software they are looking for "doesn't exist". They may not know where to look, or their search attempts fail.
Many windows users only used Internet Explorer because they didn't know any better... they didn't bother looking for alternative browsers, because they didn't know they existed. Once micrsoft were forced to display alternative browsers in EU versions of windows, Opera, Mozilla et al saw increased traffic - people were informed that alternatives exist. Now, replace "Internet Explorer" with MAS... things aren't much different.
From the users point of view who fit into the above categories - if software doesn't exist in the MAS, then why would it exist at all? Larger companies such as microsoft have an advantage of having more exposure. I'm sure a MAS version of Office isn't that far away.