This practice just seems to go against industry standards.
Industry standards are defined low enough to suit as best as possible in most of the cases, with most of the presses, most of the RIP, most of the print-shop, most of the jobs, and most of the papers, to help designers to prepare "blindly" files which will be printable in good conditions by all the printers: that's why industry standards are below (and sometime far below!) the actual possibilities of modern presses, modern RIP, modern printshops.
This printer prints postcards... and postcards are not "the industry standards" in printing, but are a particuliar case: it's difficult to print a 350% rich black on a thin offset paper... but it's easy to do on a the thick paper used for postcard: this postcard printer uses a paper that can accept the job...
... it's difficult (or almost impossible) to print a 350% rich black with a 10 years old 4-colors press that has only an infra-red dryer... but it's easy to do with a modern 4-color press with an UV dryer and the adapted inks: industry standards, with a 300% or 325% maximum TAC, are still made and adapted for "old" (10 years) presses... but this postcard printer has the last technologies that allow him to print a 350% rich black, and his presses can do the job...
... it's difficult (or almost impossible) to have a perfect registration on a thin offset paper... but it's easy to do on a the thick paper used for postcard: again the paper can accept the job, and modern presses have very efficient automatic registration systems...
... so, your postcard printer is not working with the standard industry rich black because he works on a different paper that can accept a 350% rich black, and with modern presses that can print it... so he can offer to his customers all the advantages of a very rich black!
And as a general way of working, if you know who's the printer who will print your job, you can improve your files, improve your job, or save time by dealing exactly with the real possibities and limitations of this printer... for example:
- industry standards want a 300% TAC in the pictures... but if the printer says to you that he can print 350%, you can take advantage of a better black and better contrast!
- industry standards works with 150 or 175 lpi screens... but if the printers can work with 200 lpi screen on the choosen paper, you simply need the good resolution for your pictures to take advantage of this finer screen.
- industry standards wants 1.3 PDF, made by distilling a PostScript file, with correct transparency flattenning (what is really a correct flattenning???)... but if the printer has a very good RIP, you can save time by simply exporting your PDF in 1.5 ou 1.6, leaving the transparency active... and let the printer flatten the tranparency as he exactly needs/wants.