Heck, I still find sites that don't like "nonstandard" TLDs in your email address. Try putting an address that's not .com, .net, etc and it throws an error.
The thing that really annoys me though isn't email address handling. It's credit card number and social security number entry fields.
For credit cards, the number of times you should have to specify which type of card you're entering is literally zero. All credit cards of the same type (e.g. Visa) begin with the same number sequence. Visa always starts with 4, so, if I type 4 as the first digit, just call it a Visa card. Do the Luhn checksum validation to make sure it's a valid number and that I probably entered it correctly, and try to run the charge. If it fails, then provide an appropriate error message.
For SSN fields, the thing that annoys me is that there are basically 2 common ways of entering the number: XXX-XX-XXXX and XXXXXXXXX. So many sites and apps only accept one of the two and will complain about the other. It's ridiculous, because the presence or absence of the dashes literally has no bearing on the validity of the number. Just let me enter it the way I want.
Laziness seems most likely for that reason, but, on top of that, it's not like you even have to go to Stack Overflow to find an implementation. Wikipedia has one! Wiki. Pedia.
Just take my input, run the checksum, check that my expiration date isn't in the past and that the CVV value is the correct number of digits, and just run the charge. It's not like if I mistype my MasterCard's first digit as a 4 that it's going to work anyway. Just do the checks that are feasible, and then just run the charge.
Enter number, result is: 125-535-2112 .
On the plus side it was predictable and I was able to eventually enter the number something like 2153552121 and have it appear on page as 123-555-1212. When I encountered this a second time a few days later (reordering due to DOA) I discovered pasting the entire number in allowed the 'automatic' nature to add dashes correctly.
The correct answer to me is to strip out non-numbers and then verify the number is a valid phone number (which should be easier than programmatically determining names or dates).
The worst are the companies who (somewhat strictly, to varying degrees) verify the address of credit cards. I've barely managed to always verify by shortening into a grotesque form of the address that logistically makes no sense, but is apparently just close enough to match whatever fuzzy formula is used (eg. Levenshtein distance).
I know what you mean for a different reason. Explaining that yes, my street name really starts with the word “Avenue” is getting really old.
Dear everyone: Denmark does NOT have states. Literally dozens of times have I encountered a form that absolutely requires that I input something in the state field before they will ship my stuff. A sufficiently motivated individual could traverse the major landmasses of Denmark by bicycle in about a day[0], we don't need no damn states.
I usually put in "NULL" for state, and hope something breaks.
(Also, nowhere in the world except the US has "zip codes", and about 60 countries don't even have an equivalent postal code at all...)
Well, that hasn't stopped similarly-sized Switzerland with 26 cantons. ;)
From what I can recall, the number of times I've had to specific what type of card I have when filling out an online form is zero, because every form I can remember using did autodetect it. I admit I'm fairly young (only have had a card for 10-12 years), but from the amount of frustration you seem to have about this, I feel like you must have run into it much more recently than that.