Thanks for the suggestion Maggie; unfortunatley I did grade three in November!
I think that the sightreading may be down to both being able to play by ear and the way we learnt. I don't know about you, but when I was learning the pieces that were too hard to read quickly and was playing each section over again I always went back to correct my mistakes: problem one with sightreading

. Also I think perhaps the reason we can remember things easily is that (subconsciously) we only have to remember the sound of the piece, which is a lot easier than all the notes, and that can give a good clue to what the note will be even if we don't actually remember it exactly.
I don't think it's all down to playing by ear though, my boyfriend (and teacher: and before anyone gets worried he was my boyfriend for three years before he was my teacher and is the same age as me

) has perfect pitch but he's been learning with a teacher since he was six, he can play by ear far better than me (for obvious reasons...) but he is also brilliant (sickeningly so!) at sight reading: probably because he never relied on doing that to learn pieces, I don't know though.
Perhaps we just didn't read the music for as much of the time as in the traditional approach because we'd already remembered it when we had to to play it; whereas if someone did read the music every time they practiced it they'd get more reading experience. Another problem I did get with the Beethoven is that I could only start the piece from a few fixed points: I couldn't start from just anywhere and play it and if I got stuck the music wasn't particularly much help in starting again from where I was; did you experience this or not?
Recently I've tried to stop learning the harder pieces and concentrate one ones nearer to to the level of the exams I'm doing (it's hard to do as there are so many brilliant pieces I would love to play: I've got them all lined up as when I've done grade X I can play this! Also I think that I will do a better job of them if I leave them until later) and I find that this way I can play the pieces without having to memorise the whole thing first. Having said that I do still very quickly memorise it anyway but I can't help that and I suppose it's not necessarily a bad thing, but there is now a short while there (a few days) where I can play the piece but not without the music, so I can read these pieces real-time. I did have a look at the first movement of the Moonlight sonata again the other day (I was inspired by this) and I can now definitly read it far better than I could (which is good since I've forgotten some bits) and can read the music to be of some help to me now!
All this does of course give us a good technique for exams though, if you play it through in the 30 seconds beforehand and remember what it sounds like you can do the real thing both from the music and by ear (although that assumes you get it right the first time...) but I think that I do use this technique a little.
The problem with just reading anything is that we only have harder pieces: say minimm grade two exam pieces but mostly above grade four exam pieces (never mind sight reading) around the house and I do try to read those but harder pieces encourage me to get more into the habbit of stopping to correct and don't promote fluency since they're hard to read. Having said all of this I wouldn't say I've got a big sight reading problem: I just have to work a lot harder on it than on other things!
I've never met anyone else who learnt in this way it would be interesting to know if other people do the same; I suspect it may be due to the temptation, if you can play harder pieces, to skip to higher grades and miss out the foundation stuff and just struggle with sightreading, what do you think?