Stupid CTE tricks -- string concatenation

Pretty cool little trick you've made there. With the help of an analytic function, I've fixed the ordering, and as a byproduct it also scales better:

WITH ranked AS (
    SELECT  make,model,Rank() over (PARTITION BY make ORDER BY model) Rnk 
    FROM    MakeModel
    )
,cte (make,models,rnk) AS
    (
    SELECT  Make
           ,Model Models
           ,rnk
    FROM    ranked
    WHERE   rnk = 1
    UNION ALL
    SELECT  cte.Make
           ,Models + N' , ' + Model
           ,r.Rnk
    FROM cte
    INNER JOIN ranked r
    ON cte.Make=r.Make
    AND cte.Rnk = r.rnk - 1
    )
SELECT Make,Max(Models) models,Max(rnk) cnt FROM cte GROUP BY make ORDER BY make