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Actually it has to do with the switching of the bandpass filters between color and monochrome. If no 3.58 MHz signal is present the filters are left out and the full recording bandwidth is used thus giving the 300+ lines of resolution. When the 3.58 MHz colorburst is detected the bandpass filters are switched in and everything above about 3.08 MHz is diverted to the chroma down conversion thus cutting the resolution down to the upper limits of the filters limiting the resolution to 240-250 horizontal lines, if the luma was to creep into the chroma downshift side it makes some really wierd distortions. The 250 lines for SP monochrome I suspect has to do with the chroma filters and how the signals are processed, I would have to look at the schematic to give a better explanation. It appears that the SP circuits are completely separate from the highband side. It's possible that engineering decided not to switch the filters around during highband color/monochrome being redundant and adding expense. The VO-5800 is a highband with 250 lines color, I've seen both specs published in various places. There was a medical spec VO that was monochrome only with a 330 line resolution. The 250 line limitation is the bandpass filter slope at about 3.08 MHz, the chroma side comes up at this point and is about 1 MHz wide (500 khz either side of 3.58 MHz) or 4.08 MHz. (MHz X 0.8=lines) to simplify. VHS, Betamax and Video-8 are bandwidth limited to about 240-250 lines in color recording, Betamax-1 was on the higher end of this with a faster tape speed, most of the decks would switch the filters around during monochrome to use the full recording bandwidth.
One big advantage of 3/4 over say VHS & SVHS is the video dynamic range, home grade and some of the "prosumer" VHS isn't as linear on the higher end of the luma and tends to knee and compress on the highlights. I don't know if that is design feature or flaw but it's definitely noticable. U-Matic was less about the cost compromise and focused on the professional who wasn't going to compromise on quality. Panasonic had some "pro" decks like the AG-7500 that have the higher end connectors (BNC video) but the lack of format stability made VHS unsuitable for prime broadcast. You can TBC to a certain extent but the mechanical variations once recorded are going to remain. I'm not going to trust a magazine for accuracy regardless of the source, they're not technical people and mistakes are common in advertising. RTFM (read the factory manual)
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