TP, thanks for doing this. Definitely accords with what I would have assumed.
As you pointed out, though, the "competition" for being bad has gotten stiffer in recent years, and the 2014 draft is giving a lot of teams incentive to be terrible, so it will be even harder.
The team we have now might outperform the projections in my Win Shares post if only because so many of their opponents would be even less talented.
If the Celtics really want to get a top 5 pick there's still (demolition) work to be done this summer.
One quibble -- the best "guarantee" you can get in the lottery is 1-4, so even 20 wins won't guarantee you top 3. However, most years 20 wins or fewer will pretty much assure you of having the worst record.
This year, though, I wouldn't be surprised if we see some teams challenging for the futility record (i.e. closer to 10 wins than 20).