Well, people associate the PS3 as a failure too, so being a somehow smaller failure is not a good excuse.
And it is a failure for the same reason: lower than expectation results. Both of them were expected to be clear market leaders, and they aren't.
I wouldn't say that, actually.
I think, at this point, its pretty fair to say that the Wii/DS cater to a demographic set considerably different than that of the PS3/PSP and X360, and the consistant failure to recognize the significant marketshare the PS2 still holds is a severe flaw in the analysis of anyone who does so (look at crossplat sales on it, relative to the Wii, for example. The Wii usually beats it... but not by much. Pretty odd for the "hottest" new console vs the "former" near-decade-old leader, wouldn't you say?). I realize you're not talking PS2 here -- I'm using it as an example of how blindfolded some viewpoints on marketshare really are.
Within their target markets, I actually think all 3 "next-gen" consoles are doing quite well, relative to last generation, where competitors for the same demographics as the PS2 most certainly did not match up, in terms of sales. If you merely extrapolate the current marketshares over the next 3-4 years (despite the PS3 marketshare continuing to rise), you'll see that all 3 will have done exceedingly well by the end of the generation, no matter what the fanboy comparisons say.
The PSP Go, and the entire PSP line, are doing just fine. They are not even remotely failures, except from a meaningless fanboy perspective. If the UK percentages are any indication of WW numbers, in terms of revenue generated by a handheld many forum posters considered to be "too expensive", the PSP Go did quite well for itself, and apparently boosted interest in the PSP-3000 to boot.