Though late on the draw I would like to provide a few conjectures to the list by relict9.
1) Though the demographic is mainly targeted to children, the detail could be to the dedicated fans of the anime which aired in 1997. The fans since then would at least be in their early 20s, but want to keep the little kid inside them. The romance could be a detail meant to attract the older demographic from the time the anime started.
2) Don't most males start off dense in a relationship where a girl makes the move? I'm sure they do, and I have experienced real life first hand
3) I'm sure some of us had a crush when we were ten before, and Serena is as well ten being the same age as Ash, so why not put it in the show? If anything it gives a sort of realism to the plot. (To be fair, though, it would be nice if the writers were consistent with. details like that)
4) Possibly, but there has been a somewhat kind of favoritism proposed to Serena, as opposed to the past female companions. Examples being:
- Neither Serena nor her bike were electrocuted by Pikachu
-She was invited into the party by Ash rather than insisting on tagging along
-Serena knew ash at a younger age
-Serena set out into looking for Ash without a goal for herself
The evidence could mean the writers may have something planned for Ash and Serena.