Mary Jo Foley, our resident expert on everything Microsoft, asked that question and it is an excellent one. One of the underlying currents in European politics is a policy of equality with a nice paradox of neutrality thrown in to create chaos. Makes absolutely no sense, does it? but that is the way it often happens.
Europeans are always under estimated when it come to business and government interaction and "why" they do things the way they do.
Mary Jo was wise to raise an eyebrow as to what purpose the EU would want Microsoft there and what will Microsoft testify too. Consider this: Microsoft now has 10 years of litigation experience surrounding anti-trust; MS Europe has a significant advantage when compared to Oracle.
Now let's think about this for a second... or two...
Microsoft has plenty of reasons to be there and *should* be keenly aware of the dangers that lurk when testifying before the EU, which is far more dangerous than any U.S. DOJ request and demand. It must appear so it will. But how and why are reasons the EU will manage and play out. Microsoft will tread carefully and cautiously. Any testimony they give could be ammunition against them in the future. This benefits the EU commission, not Microsoft, let alone Oracle.
Microsoft also has a good reason to be there and not because of payback, but also to observe and see how the EU rides herd on Oracle - because if there are sufficient similarities in adjudication of Microsoft's EU business dealings and Oracle's takeover of Sun (and Open Source SQL etc.) but have different outcomes, the EU may have to back pedal on its punishment of Microsoft. The EU knows this, but as is the case with European Politics - they sometimes don't care.
Google has also got into the act, submitting information to the EU - but did not disclose what it said. It should be noted that Google uses MySQL extensively in several parts of its business.
Oracle wants this thing done - too bad, they have to wait - calmly as millions get burned up keeping Sun afloat. You should scrutinize every word that comes out of the hearings... it should give you blog stories that could last a lifetime or burn up like a story out of Mission Impossible...