Chopin's Op. 10 - Relative Key Forms

[le_poete_mourant]

I was playing some of the Op. 10 Etudes of Chopin today, and I suddenly realized what his form is here.  It's a little bit like Op. 28 Preludes, in which he uses a cycle of fifths and relative minors... but there's no cycle of fifths. 

No. 1 and 2 are C major & A minor
No. 3 & 4 are E major & C# minor
No. 5 & 6 are G-flat major & E-flat minor
No. 9 & 10 are F minor & A-flat major (reversal of the major/minor)
No. 11 & 12 are E-flat major and C minor. 

There is one exception:  No. 7 & 8, C major and F major.  So, why the break?  Why connect all the others by their relative minors, yet not these two?