Plants may be sentient beings like animals so how do you decide what to eat? There is some evidence that plants are 'sentient beings' and can communicate (e.g. see this article or this wikipedia page). However Buddhists believe eating meat is wrong because of killing a living entity, what about plants? If this is true what can you eat?
Theravada and Vajrayana Buddhists (Tibetan, SE Asian) and Japanese Mahayana Buddhists are not vegetarian. So if you don't want to be a vegetarian, there are plenty of traditions that don't bother with this rule. And as for rules, there are plenty of traditions that de-emphasize rules altogether.

So that leaves East Asian Buddhism. The traditional arguments for vegetarianism are based on the traditional cosmology, which makes a distinction between plants and animals. Sentient beings can be born as animals but not plants.

If we don't believe in the traditional cosmology, the distinction between sentient and insentient remains. 

According to wikipedia, some sects see plants as sentient being-- http://en.wikipedia.org/wiki/Sentient_beings_(Buddhism) (Japanese and Tibetan, which aren't vegetarian). In Tien Tai, the founder suggested plants and even the insentient can attain enlightenment.

I'm not a radical non-dualist, but arguing that everything the same, (plants, animals, rocks) and that all states are the same (living, dead) is a typical radical non-dualist argument. The problem with nondualism applied to ethics is that it makes it easy to justify what ever you want.

And the "science" sounds like bunk. My computer feels pain when it overheats and ice cubes feel pain when they crack-- but only as a metaphor. My computer and the ice in my freezer (and the grass under my feet) has never had an original thought or even a thought. They don't have nervous systems of a sort that I'm familiar with (by my own experience of having a nervous system.)

For there to be a scientific grounding for the idea that plants (and maybe rocks) are sentient, you'd have to demonstrate that they have something similar to a nervous system and can react in the same way that a thinking, feeling creature can.  I admit a scientifically grounded interpretation of sentience still has edge cases-- for example, nematodes only have a few neurons, so they are borderline insentient.