Your wife's iPad happenend to have all the gaps with the same size, just that.
All have to have gaps, or the display would be impossible to install during production.
During mass production, it might happen some units to have uniform gaps, but that's something impossible to guarantee.
Well, impossible considering the price the iPhones are sold.
To ensure that level of assembly, the retail priced would rise several times, as all the non conforming units would hae to get back and corrected, leading to a massive decrease in daily production.
It's as simple as this.
It's all about numbers

So, yes, alhough your wife seems to have no gaps, it's just maybe the're all the same size, so no one stands out.
That's why tolerances exists, just because it's impossible to get flawless prodcution, unless manufacturer decides to produce a lot less units, whih leads to a massive retail price increase.