Weren't Metal roofs popular? And isn't the height of a structure and it's relation to other tall objects around it a factor in attracting lightning strikes?
Indeed Gravity can change and does everyday - we just can't feel it - just like we can't feel the slight changes in the magnetic field but birds and some animals can. i doubt we'll suddenly flyoff the planet anytime soon though.
Global warming didn't change the characteristics of lightning itself - it changed the characteristics of the moisture concentrations in clouds and thus Ion Characteristics - which in turn changed the characteristics of Lightning - Come now Trevor - that's Meteorology 101. lol - jk bud.