I don't agree with you... They didn't leave money on the table, they decided to focus on one thing to do it well instead of targeting everyone...
Doing cross-platform application comes at a cost (and not only in term of development time), even if it works well, the apps always feel a bit off compared to the rest of the apps on the platform (especially on mac) and that has an impact on usability, sales and so on....
Now for webapps, it's a different matter... but I'd still argue that if you are sure that a very small proportion of your userbase uses Internet Explorer 6, it might not make economic sense to support them because the cost of paying someone to do so is higher than the revenue generated by those users.
Doing cross-platform application comes at a cost (and not only in term of development time), even if it works well, the apps always feel a bit off compared to the rest of the apps on the platform (especially on mac) and that has an impact on usability, sales and so on....
Now for webapps, it's a different matter... but I'd still argue that if you are sure that a very small proportion of your userbase uses Internet Explorer 6, it might not make economic sense to support them because the cost of paying someone to do so is higher than the revenue generated by those users.