Most major defects are not found in the initial walkthru. As Tabs stated its not until you have a few days to really look around, have some wine, and test things out that problems surface. White walls hide a lot and there is just too much to look for.
We bought our previous home new from the builder. It wasn't until we moved in that a real problem was uncovered. We put some food down the garbage disposal (pre dog owners) and the sink completely plugged up - of course on a Labor day weekend. Attempts by professionals to snake were unsuccessful so they went in with a camera and found that a big spike as driven through the line - allowed only water to pass. Luckily the problem was not under our slab so it was a quick dig with a tractor to get the line cleared.
Beware of lawsuits against builders. Realize that once the suit becomes active few/none lenders will loan on that community until the suit is resolved. Known structural problems should have been disclosed - and most lenders require a full inspection. I was in a similar situation with a townhome I owned in Scripps Ranch - lawsuit went for 6.5 years - over some trival crap. Home values actually went down and distressed sellers could not get out - foreclosures. It was really really ugly. It pays to investigate the builder of your new home and drive through some of their previous communities, stop and talk to the homeowners. Most of them are very happy to voice their likes and dislikes.
We recently closed on our new home in March - last move for a long time
The builder did not allow a walkthru until close of escrow - though we did do a pre-sheetrock (framing) walkthru earlier. We have a full year to register any additional problems and so far they have been super responsive ~ 24hrs.