Care to explain these statements? They don't really jive with theory or my experience ...
First, let's make sure we're on the same page (so to speak.) Spot/CW metering on all cameras is calibrated to 12.7% reflectance. That's easy to verify...just spot meter an evenly lit white wall and take a picture. You should get a gray image with the metered area around sRGB 100, 100, 100, which is about 12.7% gray (you need a RAW converter and a "neutral" profile that doesn't apply any processing to the image.) That gives you nearly 3 stops of highlight space above 12.7% gray (12.7%x2=25.4%x2=50.8%x2=101.6%...you can't have a signal greater than 100%, so it's just a smidge under three stops.)
So let's say you have a 12.7% gray card (Lastolite makes one) or an 18% gray card + 0.5 EC (Kodak and others) or as I have, an RM Imaging Digital Gray Card (designed and marketed as a white-balance tool) + 1.3 EC (an EC amount I determined through a "calibration" process.) Any of these metering references will get you the same exact exposure.
So you spot meter your chosen reference, apply EC if called for, and take a picture. This exposure level would constitute standard exposure. Any white objects that are reflecting 90%+ of the light falling on them will be giving you a signal near saturation on the green channels. You can use something like RawDigger to see the RAW histogram. If you try to push the exposure by even 1/3 stop, you'll likely clip the green channels. This is why I say that you can't really ETTR if you have anything white in your image...because standard exposure already gets your white objects near saturation.
As for red...what I've found is that when you push red a little, even though you don't clip the channel, the scaling factors will cause the red channels to clip in the RGB conversion. So technically, the RAW channels aren't clipped, but you have to deal with the red clipping after the RGB conversion. That can be done by messing with the scaling factors and with functions such as highlight protection. I find that it takes a bit of work to get things to look right.
So my bottom line is that for most scenes, standard exposure gives the best exposure level. As I said previously...if you've got the lighting under your control then you can certain create a situation where you can overexpose by a stop or so, and then ETTR.
I think the problem that faces most people is that of being able to set standard exposure reliably. In just about any scene that's static enough to implement ETTR, you should be able to use a gray card to set standard exposure. But you do need to have a card with a good quality matte surface...otherwise the reading will be all over the place.