Grid voltage had no real impact, but the field rate of early monochrome broadcasts were locked to mains frequency, hence regional differences in frame rate.
NTSC was gamma 2.2, and PAL/SECAM was gamma 2.8, which was indeed initially partly caused by local manufacturing differences before international brands took over, but neither "standard" was really followed by anyone. In the end, concluding that it was all a total mess, we split the difference in the early 90's by formally defining both to gamma 2.4 in BT.709. As such, their curves are the same.
(Manufacturing derivation was outside the scope, as manufacturers did whatever was convenient or sold sets, going all over the place with their response curves regardless of what region they were from or targeted. This remains true today - see any new TVs standard color response.)
NTSC was gamma 2.2, and PAL/SECAM was gamma 2.8, which was indeed initially partly caused by local manufacturing differences before international brands took over, but neither "standard" was really followed by anyone. In the end, concluding that it was all a total mess, we split the difference in the early 90's by formally defining both to gamma 2.4 in BT.709. As such, their curves are the same.
(Manufacturing derivation was outside the scope, as manufacturers did whatever was convenient or sold sets, going all over the place with their response curves regardless of what region they were from or targeted. This remains true today - see any new TVs standard color response.)