Sorry to hear that, looks like Cap One is doing a pretty extensive review. I wonder if account combination is a factor in the accounts that they review. Basically, that allowed some people to create very high limits out of several cards with more moderate limits. In any case, it sucks.
A big open credit line that isn't being used is a potential liability for any card issuer, and if people aren't using the available credit then they aren't making any money. For a pretty long while Capital One was handing out $20k-$50k limits on the Venture card. I got a $30k Venture when my next highest card at the time was under $10k, so not a surprise that they came to their senses and decided to re-evaluate.
I haven't been hit yet (I haven't done any account combos because I've never been eligible) but it wouldn't shock me if they reduced my Venture. I'm pretty close to PCing before the AF hits in July this year anyway. I've moved most of my spend to other cards already, but I have tons of open credit with Capital One and with other lenders and never have much balance reporting, so it looks like I fit all the criteria for a CLD with them. One thing going for me is maybe that I have put some significant spend through in the past and that my util is always 1-2%.
Capital One: The Day The Earth Stood Still 