Complementing [Cory J's][1] answer, after some research, I found that the cartridges really have different PCB sizes.

According to [this source (2nd answer)][2], EA games PCB were slightly taller and harder to open:

Madden 93 "guts":
![Madden 93][3]


  [1]: http://gaming.stackexchange.com/a/104407/42265
  [2]: http://pineconeattack.com/2008/03/28/how-to-replace-the-game-saving-battery-to-a-sega-genesis-cart/comment-page-1/#comment-2205
  [3]: https://i.sstatic.net/MtNIF.jpg