iOS launch image for iPad: are the landscape versions mandatory?

QUESTION 1:
My app uses portrait orientation only, so I was wondering: is it mandatory to include landscape launch image for iPads?

If it is not, this would help reducing the app's memory size.

QUESTION 2:

Also, is it mandatory to include an iPad retina (3 and higher) launch image (1536 x 2048) if I am already including an iPad2 one (768x1024)?

I read in a 2 years old Adobe article that not including a 1536 x 2048 image may causes some drifting of the launch image on iPad 3 and higher, is it still the case?

I am not too concerned if the launch image is non-retina on a retina iPad, but I'd rather avoid the drifting if it is still an issue.

Unfortunately I don't own an iPad3 or higher and I can't test this myself, so I was wondering if anyone could share their experience.

Thanks in advance for any help or pointers you might give.