This is quite an interesting, and potentially 'dangerous' point for Microsoft. Great thread from OP.
I'll try and lay out my thoughts in an objective way.
Firstly, Marketplace is a service offered by Microsoft as part of Xbox Live Silver. There may be some downloads that are exclusive or time exclusive to Gold members, but the majority of downloads don't require the subscription fee to Live Gold.
Next, Microsoft, whilst obviously wanting to take a slice of microtransactions (which company wouldn't?), are stating that it's generally up to the publishers - see Tieno's post above -
"It's ultimitaly up to the publisher," he told us.
.
Taking another quote from above:-
"We've even been told that the rules of the game may vary depending on hoW much clout your company has with Microsoft.
Which publisher has most clout with Microsoft, other than themselves?
My answer: Electronic Arts.
Which publisher *currently* on Xbox Live is leading the microtransaction gouging?
My answer: Electronic Arts.
Let's just *speculate* that EA have asked Microsoft nicely to balance the content available on Marketplace to make their offerings not as much of a rip-off as they are.
To support this (Team 17 staff quote above):-
We are planning a lot of free content, but ultimately those controls are down to Microsoft because they have a lot of other companies serving downloadable content who wish to protect their 'value' (would be less so, if for example, all our stuff was free).
So how does Microsoft play this in general? Do they alienate EA? Do they alienate the
publishers or devs that want to release free content?
Remember, the original reason that EA took so long to go on Live, was that they wanted access to the customer - it may well be a stipulation in their agreement with MS to their continued participation on Live.
Whilst this speculation does not exonerate Microsoft, it certainly makes it clear to me that it is not simply as clear cut as we may think. However, I do think that Microsoft aren't entirely blameless, and they obviously side more with EA in not offering free content when they can charge for it.
Now, taking this into account, the Gears situation is even more interesting seeing that as Microsoft *is the publisher*, according to their own rules, they get the final say on pricing.
I'm not entirely sure what the publishing situation is for XBLA stuff like Geometry Wars and Marble Blast Ultra is, but if MS is the publisher, then they get the final say.
In summation, I think that Microsoft has to be more upfront with consumers as to who makes the decision on DLC pricing - if they really do have a policy that enforces price balancing on cross-publisher DLC to ensure that some publishers do not look bad, then they should state this very clearly.