Hi Tony, great question
Many people cannot afford to replace a water main so they opt for repairs if possible.
I do not understand how lead pipe even extra heavy could be used for gas service?
I think you are missing the point!
In the UK where we are located its ILLLEGAL to repair any lead water pipe by soldering!!! I dont like to see you advocating an ILLEGAL repair!
Whilst you may not understand lead being used for gas, all I can say is that in the UK its very common to still find a lead meter tail in use and very occasionally a lead run of pipe although these are very few and far between.
Tony