homework - Acidity In Organic Compounds

Why is the acidity order true?

$$\ce{CH3COCH3 > CH3CO2CH3 > CH3CON(CH3)2}$$

I deduced that in second and third option there is a $-I$ effect of the methoxy group, $\ce{N(CH3)2}$ and a $+R$ effect, too so the attached keto-carbon develops a positive charge and the conjugate base becomes unstable due to the $+R$ effect of methoxy and $\ce{N(CH3)2}$ groups.

Is my logic right?

Please tell me any explanation you can think of.