Actually the thread you reference has a fair discussion of using Perl for BIG projects. At the end of the day you can use Perl for BIG projects involving a very large number of lines of code, but it most likely is not the most productive language for that sort of use.
There is no single tool that does every job. That is just as true for languages as it is for DIY equipment. Sure, you can drive screws in with a hammer, but that's not the best way to do it. The closer the fit you get between the job at hand and the tool to do the job the easier the job is to do. Sad as it may seem, Perl is not always the best tool and one area where it is not the best tool is in writing very large applications.
Actually, discussing what constitutes BIG may be fairly important. To me a big project is 50,000 lines and up, involves more than one person and writing likely spans more than a year. YMMV.
DWIM is Perl's answer to Gödel