I agree. Our los are the same age, give or take, and we are pretty much on one nap too (although we always do two if she wakes early). Anyway, I think when there is one nap, it is important to even out the A times a bit, so the nap falls pretty much in the middle of the day.
Our routine is
7 wakeup
12 nap - usually 2.5 hrs
2:30 wakeup
7:30 bed
We did this because our lo was taking only a 20 min AM nap, and that was enough to push her PM nap out too far, so that she wouldn't go to sleep at bedtime. At daycare, that 20mins was enough to have her fighting for over an hour, and refusing to nap at all in the afternoon. So I actually made the change mostly due to daycare. I am still watching cues very carefully, so if she seems at all tired, I force two naps occasionally. If her nights are not spot on, I force two naps the next day also.
So far it is excellent though, we too are back to putting her in the cot for nap and bedtime and she drifts off to sleep peacefully instead of up to an hour of wi/pd/wo and her yelling at the top of her lungs cause she doesn't want to sleep yet.
It is very unusual for babies to drop to one nap so early, but if you are reading the cues right, and are prepared to be flexible and force two naps when you think she needs it, and your nights are unaffected, then great.
But you should really watch for overtiredness like a hawke - for NW, or early wakings, or crankiness, or having trouble going to sleep etc etc etc....that is what I am doing, and I wouldn't say our transition has been successful until things have been going great for a good month!