1. Very true - but on the other hand, you have been able to upgrade every iWork file to the next upgrade, so as long as you keep your files up-to-date with conversions with every major release, you are OK. Agree that this is not ideal.
2. Internal sharing of documents is not affected by this if you are using OSX as your front end from a top down corporate level perspective. External sharing I don't want that information presented or editable to 3rd parties in any case. Export what you want to show as a PDF, keep the data tables internal.
3. True, but if you can do Excel, you can do Numbers, and learn it well. I am not saying Excel isn't the standard, I am saying that there is no longer a compelling reason why this should be so, other than the main effort involved of actually making the switch if you are stuck and entrenched in a Windows box world.
I use Numbers seriously in the business world every day. I agree with you that major companies in well established industries with a long history cannot simply migrate, we've already been over that. I've had the advantage to be in a position to influence our corporate front end platform from a very early stage, so our switch was almost completely effortless. When I hire new people to my finance department, they have to be willing to drop Excel for Numbers. At my company, Numbers is the standard, not Excel.