There have been a number of songs written called "My dog has fleas"--and I'd hazard that they all use the uke tuning motif and came after the mnemonic was well established in the musical tradition.

Yes, you have to learn the tune first, but how long does that take? Once lodged in the brain, you never forget it or flub it--which is exactly the point. That it is so well known, even to those who have never touched a uke, proves its utility. If one doesn't know it, but is learning uke from a friend or tutor, this silly four-note "song" will probably be the first thing they teach you.

As Will Fly pointed out, the mnemonic transposes (unlike others, such as "Every Good Boy Does Fine"), so once you have the starting note, the tune tells you how to tune the remaining strings. The transposition aspect is important, because there are two base tunings in wide use: G-C-E-A and A-D-F#-B (which is just the former tuning transposed up a whole step).


The most important impact of reentrance on uke playing is undoubtedly the more clustered chord sound, and the primary mode of playing the uke is just to strum or arpeggiate chords. So it's true that neither the drone nor the alternating 4th/1st melodic style is mainstream in uke playing, but that is no reason to state they aren't important techniques. Bluegrass grew out of two-finger picking precisely because of the limitations of strict two-finger alternation. Melodic banjo grew out of bluegrass because of the choppiness of playing melodically on a single string at speed, and the uneven volume and quality when hammering-on and pulling-off. If you listen to melodic players, the difference is immediately noticeable, which is why the technique keeps gaining ground in the banjo world. Reentrance is a key aspect of its success. The same sort of shift is now occurring in the uke world (specifically, in moving away from strum-dominated playing) and players like Jake Shimabukuro are leading the shift.

In that clip, Jake is mainly demonstrating a basic strum pattern, not discussing picking patterns or melodic playing. If you examine what he's doing when he arpeggiates the strum into a picked riff, you'll see that he is indeed alternating 1 and 4 to play the melody notes, in dotted rhythm, with a chordal underpinning on 2 and 3.

Uke tuning developed as it did because Hawaiians were trying to emulate the small Portuguese guitars they first encountered, but due to the limitation of materials they had to work with (strings of nearly uniform constitution) they had to transpose the bottom note up an octave. If you transpose the standard uke G tuning down a fourth and drop the 4th string an octave, you end up with the pitches of the top four strings of a guitar. So the primary reason for reentrance on the uke is historical, not a product of intentional design to facilitate finger-picking. Nevertheless, as melodic playing becomes increasingly popular in the uke world, the advantages of the reentrant tuning become more fully exploited.