Hi 
Yes. With regards to paragraph 1 with the amendment that i think you mean MSO 2010 rather than the non-existent MSO 2012. There is a version for Mac called 2011 but that is really just 2010 redone for Mac and it takes them about a year to do that. MSO just doesn't develop that fast. It's typically 3 or 4 years between releases which is one reason they have such problems with security and need such frequent patches.
For the 2nd paragraph neither option is optimal. It's why almost all of us on almost all lists recommend keeping an original in ODF but use "Save as" to to the older MS formats when sharing with other people.
When people start using LibreOffice there is no need for them to ever buy a new version of MS Office. They can keep using their ageing one if they feel the need but will probably find they 'need' it less and less as they get used to doing everything with LibreOffice and other OpenSource tools.
It is generally considered extremely foolish to get rid of the old suite at least until after "the end" of the migration process. It's what MS recommends.
For their own products they mitigate against the problems by offering training and encouraging people to become "Microsoft Certified" in the new version. It costs quite lot. The training, books, certificates are all published by MS and each is quite expensive. It builds-up the "blame the user" culture of the MS world.
During a migration even quite hefty bumps in the road are easy to work-around by using the older tool that you are familiar with. That gives the user plenty of time to work out how to deal with the bump in LO. It might be something simple that most people don't use, such as not knowing where "undo" is in the menu ("Ctrl z" or "right-click and undo" are usually faster than moving the mouse up to the top of the screen).
If the user had followed the idiotic "Microsoft-world advice" of getting rid of the old then not knowing how to "undo" could then de-rail the move away from MS products and with an added push of stupid advice form the MS world could rack up extra costs of re-purchasing old versions of MS Office again.
So, the usual advice within the OpenSource world and given to newcomers is to keep the old version near at hand while trying out the new version. For OpenSource products it's not an issue because all the various options are cheap and easy so you can uninstall, reinstall, test-drive, virtualise, parallel install (alongside), LiveCd it and back again without having to repurchase or re-license anything. For MS products it means not uninstalling in the first place.
Just in case anyone thinks my example of the "undo" was too idiotic and foolish i have to say i agree completely. Every time it happens i just shudder or laugh. The last example was a German (?) city that then went and reported to the press blaming LO but in the course of the article it became obvious that the city had been extremely foolish (and that it wasn't even LO that they had been upgrading too).
So, no don't buy new versions of MSO but also don't entirely switch to always using ODF. At least, not yet. Be sensible. If your organisation has LibreOffice installed for everyone then you can stick to using ODF internally but when sending documents to people outside of your organisation you will have to use an MS format. The new ones are rubbish (ime) so stick with the older MS formats (for MS Office Xp, 2000, 2003, 98 etc) because everyone can read them.
ODF usage is spreading and becoming more common-place but many people still stick with the whimsical nature of the MS formats that change unpredictably and never quite work the same way on any 2 machines due to random changes of a single company.
The "therefore" in e-letters post is patently absurd. Again. Instead try
c) Give people a link so they can download LibreOffice, perhaps the portable version
d) Use ODF for yourself, for your own use, for your main copy of the file and then share by first taking a snapshot of your file in MS format = "Save as MS Xp format"
Regards from
Tom
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), after opening in m$ excel 2010 (yes, m$ can open ods