I think one of the reasons for averages increasing in the recent years could be the fact that there are many more resources out there for students (internet, CD-ROMs, prep. courses for the DAT, etc.) that can help them learn the material better.
With regard to averages, granted they do give you an idea of what to expect, but in the end they are just "averages" of ACCEPTED students. By definition of an average, 50% of scores are above it, and 50% are below it. One of the main problems with averages is that they can be distorted by extreme scores, whether on the high or low end, especially with a small sample size (50 - 100). For example, if a dental school lets in four students with a 4.0 and six students with a 3.25, the class average is 3.55. Unless your GPAs and DATs are WAY below a school's average, I don't think it would hurt to apply, especially if you have lots of research/dental exp, extracurricular activities, etc. Just my $0.02.
Eric