Audience - how much does it matter?

This is just my humble opinion, but the more I think about audience, the less I think the differences really matter - at least in terms of instructional design. Let me explain... 

My audience for training materials at work is primarily sales representatives and surgeons. 

• They are very busy professionals with lots of demands on their time and attention, yes. But who isn't? Even if you're a kid who doesn't have a job, you still are busy, with lots of demands on your time and attention. Those demands might include video games, sports, playing outside or thinking about what you'll ask for for Christmas, but they are still things a kid wants to think about. This aspect of my audience makes me try to reduce the time they are required to spend on training - especially trying to reduce any extraneous things that they don't really need to know or do in order to do their jobs more efficiently & effectively. What I'm saying is, always keep focused on the "need to know/do," don't limit that focus to the audience you think is "very busy."
• Related to the "busy" aspect, I also want to provide my audience the ability to get straight to the information/practice that they feel is important to them at that moment.  I want to give them control over their learning experience so that they can skip things they already know and focus on material that is new/essential.  I realize that sometimes our clients or SMEs want the learner to see all the information, but if we're assessing their performance at the end, we shouldn't need to force the issue.  They are adults, and failure isn't always a bad thing!  We can learn more from failure than success, and as long as you give the audience the control to go back and review or practice, it will be a more meaningful experience.  Actually, I even think this one holds true for kids - give them the control & let them direct their own learning, you can't force it anyway.  So again, give all audiences control of the learning experience, not just the "busy" ones or the "adults," etc.  All audiences are going to learn more by self-direction, when you provide the resources and practice opportunities they need.
• They also have a widely varied and complex job to do, in fact it seems so complex to me, I would never want to attempt either job myself.  But again, who doesn't? Are the jobs of an engineer or administrative assistant or instructional designer any less complex if you really break it down?  Probably not.  None of us live in a vacuum, and the complexity of our environment is universal.  This aspect of my audience leads me to try to break things down to the steps and building blocks of what they need to know/do, and build it back up to at least a somewhat-close approximation of a real scenario where they can practice application of the new skill.  Again, always provide this break it down & build it up process in your instructional design, don't limit it to only the audience you think has a "complex" job.

I will concede that language and culture aspects are always going to make a difference, and content is of course going to affect the ultimate design, but a lot of aspects of your audience really don't change much about a meaningful instructional design in my opinion.

What do you all think?  Have you found the differences in audience really change how you design your instruction?  Or, do you agree that mostly the specific aspects of the audience don't affect your design that much?