I think that to the contrary, that it would allow people to determine whether the original results were due to flawed software by analyzing the code. Subsequent efforts would remain free to create their own implementations from scratch if desired.
and that brings us back to why many scientists don't publish at all now...
As long as not publishing code is standard, there's a incentive to do it since it might open you to career-withering criticism...
I have tried to explain (With limited success) to my colleagues in bioinformatics that not unit-testing your code is like using an instrument that hasn't been calibrated, and blindly trusting the results to be right.
This is the standard procedure for when you've developed a complex algorithm to do something novel, and actually working through it by hand would take hours.
I should know, this is how I used to do it before I knew better, and as a result one of my published papers has (very slight) numerical errors in.
A lot of time might be wasted going down that path too.
The quality issues aren't all that different than a web framework, either. Release one or a small number of code bases, and have everybody pound on and improve them, and you might get somewhere. Have everybody write their own code bases from scratch every time and you'll get yourself the scientific equivalent of http://osvdb.org/search?search[vuln_title]=php&search[te... .
To be honest at this point when I see a news article that says anything about a "computer model" I almost immediately tune out. The exception is that I read for some sign that the model has been verified against the real world; for instance, protein folding models don't bother me for that reason. But this is the exception, not the rule. When it became acceptable "science" to build immense computer models with no particular need to check them against reality before running off and announcing immense world-shattering results I'm not exactly sure, but it was a great loss to humanity.