I wrote a post about this topic a few weeks ago, asking to what extent a new political era necessitates alterations in interpretations of the Constitution. While judicial conservatives read for literal statements, judicial liberals have a more flexible reading. The argument centers around whether laws written so long ago can be applied in the present day. Can we assume that the founding fathers WOULD HAVE written the laws this way, had they known the situation today?
In response to Peter's post, the "legality" of cases such as Roe v. Wade is really a matter of opinion depending on how closely one reads the Constitution. Like I wrote above, times have changed since the Constitution was written, and whether the same wording can apply today is the debate I think you questioned. It seems like you are a judicial conservative since you argue that cases like RvW were decided on "perceived rights." That right is the "right to privacy," which can be applied to every Amendment (1st Am. is "privacy of beliefs," 3rd Am. is "privacy of the home," etc.).
That so many cases were ruled on interpreted rights such as that of privacy may suggest that there was a trend of the Supreme Court toward judicial liberalism in those times. Sandra Day O'Connor, who became part of the SC during Reagan's presidency, was perhaps one of the contributors to this trend. She was "soft on abortion," which was likely an important factor in the passing of Roe v. Wade.