Katy Perry had a head start, and had the biggest hit of the Summer with "I Kissed a Girl" in 2008. Her album debuted in the top 10 and she was doing great.
On the other hand, Lady Gaga had a slow start. Her first single was lingering, and out of no where it became a huge hit. Her album was a sleeper hit, and took months to enter the top 10. It ended up outselling Katy's debut.
In all seriousness, Katy's first single didn't get any media attention, until Madonna talked about her. IKAG smashed cause it's a generic catchy song. Gaga smashed cause she dressed incredibly weird and had shock value
The wigs, the outlandish outfits and just her overall image - all of it is very 'Europop' inspired in a way - so that's kind of what wins the people over in Europe. Asia tends to love all that too.
It's not really the music, even though Katy is more strictly 'American'.
And this didn't? Plus whip cream coming out of boobs, and other things.
The irony that all this occurred after Gaga's peak (so-far). Katy remains the Christian school girl and people were just more interested in Gaga - she had the message as well as the sales.