I never got the impression that WOTC hated all 3PP products.
Indeed, they WANT adventures produced. What WOTC found annoying my guess was that "supplementary rules a.k.a monsters/feats/etc" products were competing directly with their own products.
That's NOT what WOTC wanted for the OGL IMO.
When integrating a 3pp product with a WOTC product into a campaign is the same diffculty (as it was during 3.x era), there's no great incentive to choose the WOTC product over the 3pp product.
When even DRAGON AND DUNGEON material gets incorporated into DDI for 4e (as mentioned earlier, how does this work if Paizo ran both magazines still), yeah, the WOTC product is likely to be more chosen.
As an aside, it should be mentioned that DDI might also be possibily cannibalizing sales from WOTC dead tree line. On 4e forums here, @ penny arcade, @rpg.net etc, when asked by people "what products should I buy?".
The answer is usually..."PHB (might be ESSENTIALS soon), DMG and then get yourself DDI."
(hell, we don't even mention MM and if you're an old hat DMing, I'd drop buying the DMG as well)