An alpha blended sprite is where instead of having a choice of whether a pixel is transparent or not, you have a choice of various levels of transparency. This allows you to do lots of clever things ranging from having sprites of ghosts that show proportion of the background through them to making the smoothing around the edge of icons work correctly (generally RISC OS sprites are blended to grey so that they look nicer in the Filer, but this makes them look horrible on fancy pinboards - now you can have the edges correctly semi-transparent so it looks better on any background [are you listening RISC OS Ltd?]).
Anyway, the (apparent) reason why many Select features cannot be ported across to RISC OS 5 without much work is due to 'low level kernel changes'. I can appreciate this for many of their changes, but that line simply doesn't apply to the alpha sprites unless they've done it in an insanely perverse manner. I'm sure I'm sounding like a broken record with this issue, but it's directly affected me and many hours of my evenings because of this idiotic policy of theirs. As is probably becoming very apparent, I've absolutely no time for RISC OS Ltd because of their constant failure to decide upon a development direction, see where the market is going, or even do simple things like provide documentation for the enhancements/changes they have done.
Having said all this, I'm not especially happy with Castle developing RISC OS. It's nothing to do with any of the same reasons though - they've proven themselves to be everything the market could want them to be - my issue is that we're going back to the days of Acorn with the OS developer also making the hardware. And please can everyone not now hijack this forum and start moaning about the competition being MicroDigital and an Omega that they saw (heck, possibly even touched!) at a show once that seemed to go wrong when they did something that they can't remember but they've also heard that everyone else has a buggy one so it must be true and any user who has one that's been nigh on flawless is either insanely lucky or a liar, as I'm talking about the principal of having more than one hardware developer and not specifics.