Uhnn... The SEGA Master System has been my very first home console, and every time I see a photo showcasing SMS games... Man, the nostalgia. And the subtle desire to start collecting again for that system too.
What stops me is the fact I couldn't go PAL, now, and prices for Japanese SMS (boxed, complete and in nice conditions) seem generally pretty steep.
PAL is 99% safe when it comes to SMS, since Sega did almost no optomisation for PAL
at all. A very simple 60Hz mod on a PAL machine and you're laughing.
Of course PAL (and US) boxes for SMS range from hilarious to hideous, and even though they started with consistency with the grid motif, this devolved dramatically to the point it's one of the least consistent box ranges. You can see it in davidwhangchoi's pictures above - Alien Syndrome is oldest, and uses the stardard typeface for the game name, and a picture superimposed just over the grid. Shinobi are R-type are the next evolution, and get their own title font and the picture 'taking over' the background. Early games had a simpler graphic for the picture, and late games completely abandoned the motif altogether.
Even the name of the system effectively changed in all countries, obviously in Japan from Mark III to Master System, but in US/PAL the first half of the console's life the games (and even console packaging) had no Master System branding and it was simply 'The Sega System'. See all three games pictured above, no Master System name on the cover at all, and even the back and manual referred to the system as either just 'Sega' or 'Power Base'. Master System was confusingly referred to as just the console (like the NES 'Control Deck'), and even that had two names, Master System and Power Base (it literally says on the top 'Master System/Power Base'), and they usually used the latter term in manuals and marketing and packaging, but 'Master System' was also confusingly used to refer to a particular set which included the light gun (so an equivalent of the NES 'Action Set'). Also see above for this in action, the converter for Mega Drive/Genesis isn't called the Master System converter, it's called the Power Base converter.
I guess the summary is Sega had no idea what they were doing, so business as usual for them.