4 inches is standard thickness for residential driveways in Indiana.
As others have stated, it is rare that wire mesh, either roll or mat,
is located properly in the middle of the slab with sufficient cover to
avoid corrosion. I would suggest fibers instead of mesh. The fibers
make the concrete mix more homogenous, and reduce cracking during the
placement and curing of the concrete, so that there are fewer cracks in
the final product. Make sure that the contractor is placing joints no
more than 10 foot apart, and as square as possible, and is placing
expansion material between the driveway and any other structures or
Curing is the most neglected and one of the most important steps in
installing a quality concrete driveway. A driveway installed with 4000
psi concrete mix, properly finished but not cured properly, will have a
top surface of 2500 psi concrete that is very porous, and it will be
more likely to have surface defects with freezing and thawing, and
especially with de-icing chemicals.
The Indiana Ready Mixed Concrete Association, (where I work), is a
Non-Profit organization promoting quality ready mixed concrete in
Indiana. We have residential concrete guidelines available for
homebuilders, contractors, and homeowners. You can go to www.irmca.com
to get in touch with us.