Gerard, tell me about it.
It's hard to find anyone who has even seen "ISO 8601" so there is not general compatibility between tools that accept "ISO 8601 (date)?(times?)"; the xsd:datetime (defined mainly as a restriction of ISO 8601) is closer to an open standard, but people aren't so sure about extra digits in the date fields, but maybe we will need them to deal with the year 10000 problem.
IEEE 744 is a similar scandal since it hasn't been read by most developers, particularly systems developers, so it is unlikely that FP operations in your favorite language are completely conformant.
Now IEEE does have the Get802 program which lets you get slightly aged documents for networking standards and ISO does release the occasional standard for free such as ISO 20222 but there is a big difference between those two and the other organizations like the OMG, W3C, IETF, and FIPS that publish standards for free and manage to somehow pay the bills.