I've bought various terminators over the years. Most of my work is at 10 MHz or less so just about anything will work. But I've measured some terminators that are likely 10base2 at higher frequencies so I'd know which ones to grab if I needed to. At 100 MHz, they all had a return loss > 30 dB (VSWR < 1.06). At 1 GHz, they varied from < 8 dB (>2.3) to > 18 dB (< 1.3). I've also measured various unmarked SMA terminators. They all measured > 28 dB @ 1 GHz. To make the measurements, I used a signal generator, directional coupler, and RF power meter. Calibration is questionable so take the actual numbers with a grain of salt.
I suspect that if you tore apart a name-brand multi-GHz rated terminator, you'd find a very special style of resistor. Maybe a circular resistor that would be comparable to an infinite number of resistors in parallel instead of two or three resistors. Continuous soldered ground around the outside, no discontinuities anywhere, etc.
Bottom line, if you can measure your terminators, or you work at low frequencies, 10Base2 might be all you need.
Ed