You are right. Unlike with the ZX81 cassette storage wasn't essential though as all the Pocket Computers I have owned (the first being an FX850 bought new) have had battery backed RAM. One had a clever arrangement in the battery compartment to stop you from accidentally removing both batteries at once, which could have lost your program. Of course many had very limited memory so a Cassette Deck would have been useful if you had quite a few programs you regularly ran. As you say many of these computers were used for serious real world tasks. Laptop Computers were only just starting to appear, and cost £1000s (apart from oddities like the TRS80 portable that were just a bit better than the pocket computers.
I seem to remember a ton of "oddball" programs pre-recorded on cassettes. They were great for multi-formula number crunching, some of my first computer games, that I created, were games similar to Dungeons and Dragons, where moves and battles were made on rolls of multi-sided dice. My first computer, a ZX81 used cassette but I was extremely happy when my Apple II+ showed wrapped up with a disk drive. I still used a cassette drive once in a while for older programs.
TDK Gold Tape....Not For Sale Version... This looks like an award, I don't think the hubs will work on a normal deck. https://www.ebay.com/itm/TDK-Gold-c...ault&brand=TDK&_trksid=p2047675.c100008.m2219
A couple JVC Signs. https://www.ebay.com/itm/Vintage-JV...479347?hash=item52352d4c33:g:T-8AAOSwnvpewWzC https://www.ebay.com/itm/Vintage-JV...680184?hash=item42136be738:g:63MAAOSwwJ1eUyBe
Budweiser Cassette Tape, perfect for a beer and boombox photo! https://www.ebay.com/itm/Budweiser-...BBEV2bDemotion&_trksid=p2047675.c100005.m1851
Another Walkman Shirt, this one is XL https://www.ebay.com/itm/RARE-Vinta...rentrq:7a5eb22c1720a6e6abb2f21cfff2fe21|iid:1
While the asking price is far too high for me, there are some interesting pictures (like this portable CD setup) in this 1985 Sony Brochure https://www.ebay.co.uk/itm/SONY-198...501358?hash=item1ce6b1e0ae:g:BqkAAOSw8NNeexu3
Boxed Panasonic RX-HD10 Dual Deck Personal Stereo (for making copies of your Spectrum tapes in the playground ?) https://www.ebay.co.uk/itm/PANASONI...213245?hash=item3b3e88a5fd:g:Xi0AAOSwXOtdg4GB
Sony Walkman Tape Cleaner, this looks like somebody may have put it together for a promotion, it would have been a nice freebie back then. https://www.ebay.com/itm/Sony-Walkm...263751?hash=item1f10e27907:g:ZrwAAOSw7WBe1bKg
I can't remember if I've seen a Walkman Branded Blank Tape. https://www.ebay.com/itm/SONY-Walkm...ult&brand=Sony&_trksid=p2047675.c100008.m2219
This is interesting, an FM Cartridge that looks like it will work in most players. Most FM cartridges only worked in one brand and had extra connections so you didn't need to hit the play button. I always like portables with a radio because the battery life is pretty short but the radio would keep going for a few more days, unfortunately with this style, the power-hungry motor is still turning. https://www.ebay.com/itm/KAP-X-07-C...a=1&pg=2047675&_trksid=p2047675.c100010.m2109
The best tape ever made? The Sony C-60SMMST Super Metal Master Cassette. These tend to go for big money, it would be interesting to hear if anybody has used one. https://www.ebay.com/itm/Sony-Super...257734?hash=item263e04c706:g:n4MAAOSwVkVeqOJV
An even biggesr problem is how do you get to the tuning knob when you have put the cassette in the player ?
Quite a few things for the MiniDisc fans https://www.ebay.co.uk/sch/mr_mini_disc/m.html?item=233622005028&rt=nc&_trksid=p2047675.l2562
Nice Longman, too bad he doesn't ship to the USA, a real minidisc boombox! Almost, it looks like it doesn't take batteries but it's close. https://www.ebay.co.uk/itm/RARE-KEN...158749?hash=item3664e7fb5d:g:OQ4AAOSwcble6N9w
I posted some information about this a while back, it's not a boombox but kind of looks like one and check out how thin it is. This is the first time I've seen one up for sale, the Sharp SC-1250HB. https://www.ebay.com/itm/Sharp-SC-1...743262?hash=item23d98cde9e:g:-U8AAOSw07Be6QT-
I was trying to work out what the power bulge on the back was for then realised it is probably for the cassette motor. Of course the innards of many Amstrad systems were similarly thin but they put them at the front of a full depth stack system to look the part, and support the turntable at the top.
It wouldn't surprise me if Sharp had a huge motor in there, these photos suck but I think it was pretty expensive when it came out. I would splurge on this and even more on the Technics Slim System.
Interesting, I didn't know there's this gold-ish version. The silver ones pop-up quite frequently where I live, though most are missing the speakers. I've seen like perhaps 4 in the past 2 months. I think it looks better in silver, though.
The seller with the mini disc boombox is also selling another mini disc boombox made by Sharp with 3 Cd changer here are the details https://www.ebay.co.uk/itm/VERY-RAR...005028?hash=item3664f4e524:g:yQ4AAOSwRkhe6iFZ