Mendelssohn: Prelude and Fugue in G major, Op. 37, No. 2

I recently watched a Gresham College lecture titled The German Revolution in English Organ Technology.  Mendelssohn had a lot to do with some of the changes that were effected (he was "a catalyst... [who] open[ed] people’s ears to the possibilities of organs from abroad and a new way of building English organs"), and his Prelude and Fugue in G major, Op. 37, No. 2 was used as an example.  I'd heard this piece before, but listening to it then, I thought I noticed something, so I consulted the notation.

At the beginning of the fugue, there are pairs of half-steps:

(click the image to enlarge it)
(notation found here)

In the second measure of the pedal part, there's C to B and then F to E.  Bridging the fourth and fifth measures, there's G to F# and then C to B in the left-hand.

I'd thought I heard the B-A-C-H motif, which is also comprised of two descending half-steps (Bb to A and then C to B).  Obviously, this isn't the same, but it is similar.  Mendelssohn knew Bach's organ works, and the lecturer mentioned Bach's influence on Mendelssohn's own organ works, so I'm wondering if his inclusion of those descending half-step figures is an indication of that influence.  It'd certainly be a minuscule indication, but I still felt it worth noting, for myself if for nothing else.

Brahms: Piano Concerto No. 2 in B flat major, Op. 83

Every year, I listen to the 22 LPs in Funk & Wagnalls' Family Library of Great Music.  Usually, I do this in May, but for lengthy and uninteresting reasons, this year I'm listening to them in June.  To-day, it was Brahms' Piano Concerto No. 2.  I've listened to this only a couple times, but this time I noticed something in the first movement.

Starting at about bar sixteen of the D section, there are octaves in the piano part:

(click on the image to enlarge it)
(notation found here)

I'm not sure if it's meant to, but it reminded me of the B-A-C-H motif.  Brahms has Ab G, E Db, and then Gb F.  It's like Bb A C B in that there are sequential descending half-steps.  I don't know very much about Brahms, and the resemblance here might just be a coincidence, but - if nothing else - it's given me a reason to become more familiar with the piece.