Cech & Cudicini >>>> Howard & Carroll & probably any keeper United propose to sign.
Ferreira, Gallas, Johnson, Bridge, Terry, Carvalho & Huth. 7 defenders to United's 6 & United have no claims of supremacy so quanitity does matter here. Although, it is noted that you left out Phil Neville.
Makelele, Lampard, Tiago, Cole, Duff, Robben, Geremi, Smertin & Jarosik & Parker. 10 midfielders to United's 5. And while Makelele can match up with Keane & Lampard with Scholes, Robben is better than Ronaldo & Giggs & Duff is their equal. And all the midfielders named here are at least equal to Fletcher with at least 5 being undeniably better.
Drogba, Kezman, Gudjohnsen, Forssell. 4 strikers to United's 3. Now, none of these guys are as good as Ruud. Kezman would have the best chance of matching Ruud - if he were on form. On current form, Rooney is a better player than these guys but I wouldn't place him above Gudjohnsen in terms of hitting the back of the net - keep in mind, the Iceman played in midfield this season. However, I believe all the Chelsea strikers to be better than Smith.
It also worthwhile to note that Chelsea have Veron & Crespo at their disposal too.
Let's not forget to put this in context either: Chelsea have the funds to vastly improve their squad any time the transfer window is open. United do not have this luxury. So if either team is going to be improved through transfers, Chelsea are the more likely. Also, a few of those you named are not getting any younger. Neville, Keane & Scholes will all be very hard to replace. Obviously, Keane is the only one impending but still, how can United improve when they do not have the resources to replace their best players?